<PAGE>

                    [LETTERHEAD OF WILLIAM BLAIR & COMPANY]


                                                                   Exhibit 10.12


                                 July 17, 2001


Mr. Phillip S. Dingle
Chief Executive Officer
PlanVista Corporation
PO Box 30098
Tampa, FL 33630-3098

Dear Phillip:

This is to confirm the additional engagement of William Blair & Company, L.L.C.
("Blair") by PlanVista Corporation (the "Company") to render certain investment
banking services in connection with a possible business combination (through
tender offer, merger, sale or exchange of 50% or more of the outstanding capital
stock of the Company to persons who are not owners of more than 10% of the
Company's common stock as of the date of this letter, or sale of all or
substantially all of its assets or otherwise) of the Company with another party
or a recapitalization of the Company or similar restructuring (the "Possible
Transaction").  This letter is intended to broaden the scope of the engagement
defined as the April 19, 2001, letter agreement between the Company and Blair.

The foregoing notwithstanding, Blair acknowledges that if Bank of America Corp
                                                          --------------------
and/or any of its subsidiaries provide a firm commitment to fund the senior bank
------------------------------
credit facility and any of the subordinated debt and such commitment is
delivered to the Company on or before August 10, 2001.  Then Blair's Debt
Placement Fee and Debt Restructuring Fee, as contemplated in our April 19, 2001
letter agreement, shall not exceed $250,000.

Notwithstanding the foregoing, Blair will also receive a Debt Placement Fee,
payable at closing, for any debt financing placed by Blair.

     1.   Services to Be Rendered.  Blair will perform such of the following
          -----------------------
          services in connection with the Possible Transaction as the Company
          may reasonably request:

          a.   Blair will familiarize itself to the extent it deems appropriate
               with the business, operations, financial condition and prospects
               of the Company;

          b.   Blair will assist the Company's management in (i) developing a
               strategy for pursuing a Possible Transaction involving the
               Company and a list of possible participants in the Possible
               Transaction (it being understood that such participants may
               include parties to whom Blair has rendered or is now rendering
               investment banking services), (ii) preparing a descriptive
               memorandum that describes the Company's operations and financial
               condition and includes current financial data and other
               appropriate information furnished by the Company (as amended and
               supplemented from time to time, the "Descriptive Memorandum") and
               (iii) contacting and eliciting interest from those possible
               participants expressly approved by the Company;
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                                      -2-

          c.   Blair will participate with the Company and its counsel in
               negotiations relating to the Possible Transaction, and in
               coordinating the due diligence and closing process of any
               Possible Transaction;

          d.   Blair will participate in meetings of the Board of Directors of
               the Company (such participation to be in person or by telephone,
               as appropriate) at which the Possible Transaction is to be
               considered and, as appropriate, will report to the Board of
               Directors with respect thereto; and

          e.   If requested, Blair will (i) render an opinion (the "Opinion")
               (such Opinion will be in writing if requested by the Company ),
               as to the fairness, from a financial point of view, to the
               Company's common stockholders of the consideration to be received
               by such stockholders or the exchange ratio, as the case may be,
               in the Possible Transaction or (ii) advise the Board of Directors
               that Blair is unable to render an Opinion due to the inadequacy
               of such consideration.  The Opinion will be in such form and with
               such qualifications as determined appropriate by Blair.

          In connection with Blair's activities on the Company's behalf, the
          Company agrees to cooperate with Blair and will furnish to, or cause
          to be furnished to, Blair all information and data concerning the
          Company, any Possible Transaction and any possible participant (the
          "Information") which Blair reasonably deems appropriate and will
          provide Blair with access to the Company's officers, directors,
          employees and advisors.  The Company represents and warrants that all
          Information made available to Blair by the Company with respect to a
          Possible Transaction will be complete and correct and that any
          projections, forecasts or other Information provided by the Company to
          Blair or to any possible participant, any other party to a Possible
          Transaction, or contained in the Descriptive Memorandum will have been
          prepared in good faith and will be based upon reasonable assumptions.
          The Company agrees to promptly notify Blair if the Company believes
          that any Information which was previously provided to Blair or to any
          possible participant has become materially misleading.  The Company
          acknowledges and agrees that, in rendering its services hereunder,
          including, without limitation, assisting the Company's management in
          the preparation of the Descriptive Memorandum, Blair will be using and
          relying on the Information (and information available from public
          sources and other sources deemed reliable by Blair) without
          independent verification thereof or independent appraisal of any of
          the Company's assets or those of any possible participant.
          Furthermore, in evaluating each possible participant, Blair will be
          using information contained in public reports and possibly other
          information furnished to Blair by such possible participant.  Blair
          does not assume responsibility for the accuracy or completeness of the
          Information or any other information regarding the Company, any
          possible participant or any Possible Transaction.  If all or any
          portion of the business of the Company or any possible participant is
          engaged in through subsidiaries or other affiliates, the references in
          this letter agreement to the Company or the possible participant will,
          when appropriate, be deemed also to include such subsidiaries or other
          affiliates.

          In order to coordinate most effectively our efforts together to effect
          a Possible Transaction satisfactory to the Company, the Company and
          its management will promptly inform us of any inquiry they may receive
          concerning the availability of all or a
<PAGE>

                                      -3-

          portion of the stock or assets of the Company for purchase. Also,
          during the period of our engagement, neither the Company nor its
          management will initiate any discussions looking toward the sale of
          all or a portion of the stock or assets of the Company without
          informing Blair.

          The Company and Blair will each have the right to approve the
          Descriptive Memorandum and, to the extent relevant to or otherwise
          affecting Blair's services to be provided hereunder, other written
          communication from the Company or any person acting on its behalf in
          connection with the Possible Transaction.

          It is further understood that any advice rendered by Blair pursuant to
          its engagement hereunder, including any advice rendered during the
          course of participating in negotiations and meetings of the Board of
          Directors (or a Special Committee thereof) of the Company, as well as
          any written Opinion rendered and any written materials provided by
          Blair, will be solely for the benefit and confidential use of the
          Board of Directors (or a Special Committee thereof) and will not be
          reproduced, summarized, described or referred to or given to any other
          person for any purpose without Blair's prior written consent.

     2.   Fees.  The Company agrees to pay Blair a fee of $250,000 promptly
          ----
          after Blair at the Company's request (i) advises the Board of
          Directors (or a Special Committee thereof) in a written opinion as to
          the fairness, from a financial point of view, to the Company's
          stockholders of the consideration to be received by such stockholders
          or the exchange ratio, as the case may be, with respect to the
          Possible Transaction or (ii) advises that it is unable to render an
          opinion to such effect.  In the event that the Possible Transaction is
          consummated, the Company will pay or cause to be paid to Blair a fee
          equal to 2.0% of the total consideration received by the Company and
          its stockholders as a result of such consummation (the "Transaction
          Consideration"), subject to a minimum fee of $750,000 and a maximum
          fee of $2.0 million.

          For purposes of this letter agreement, the term "Transaction
          Consideration" will mean the total amount of cash and the fair market
          value of all securities or other property paid or payable directly or
          indirectly to the Company or any of its security holders in connection
          with a Possible Transaction which is consummated, including, without
          limitation, (i) amounts paid (A) pursuant to covenants not to compete,
          employment contracts, employee benefit plans or other similar
          arrangements (B) to holders of any warrants or convertible securities
          of the Company and (C) to holders of any options or stock appreciation
          rights issued by the Company, whether or not vested; (ii) the total
          amount of indebtedness for borrowed money or similar non-trade
          liabilities or obligations (including pension liabilities, guarantees,
          capitalized or operating leases and the like) of the Company repaid,
          retired, extinguished or assumed in connection with the Possible
          Transaction, or which otherwise remains outstanding with the Company
          or any affiliate thereof as of the closing of a Possible Transaction
          or which is assumed by the acquiror or an affiliate thereof; and (iii)
          in the case of a sale of substantially all the Company's assets, the
          total consideration paid for such assets plus the net value of any
          current assets not sold by the Company.
<PAGE>

                                      -4-

          Amounts paid into escrow in connection with any Possible Transaction
          will also be included as part of the Transaction Consideration and the
          portion of Blair's fee related to such escrow payments will be payable
          upon the establishment of such escrow.  Transaction Consideration also
          will include the aggregate amount of any dividends or other
          distributions declared by the Company with respect to its stock after
          the date hereof, other than normal recurring cash dividends in amounts
          not materially greater than currently paid.

          The fee payable to Blair upon consummation of a transaction involving
          a tender offer or other purchase or sale of stock will become payable
          by the Company when control of 50% or more of the Company's
          outstanding common stock is acquired by an entity other than a current
          stockholder.  In that event, such Transaction Consideration will be
          calculated under the above definition of aggregate Transaction
          Consideration as though 100% of the outstanding common stock on a
          fully diluted basis had been acquired for the highest per share amount
          paid in the transaction in which control is acquired.  Nevertheless,
          our services pursuant to this letter agreement will continue after
          control is obtained to assist you with a second step merger, if any,
          or similar transaction.

          If any portion of the Transaction Consideration is paid in the form of
          securities for which a public trading market existed prior to
          consummation of the Possible Transaction, the value of such
          securities, for purposes of calculating the Transaction Consideration,
          will be determined by the closing or last sales price for such
          securities on the last trading day prior to the consummation or
          effectiveness of the Possible Transaction.  If such securities do not
          have an existing public trading market, the value of the securities
          will be the mutually agreed upon fair market value on the day prior to
          the consummation of the Possible Transaction; provided that promissory
          notes or other debt obligations will be valued at the face amount
          thereof.

          The fee payable to Blair upon consummation of the Possible Transaction
          will be payable in full, in cash, upon the closing of the Possible
          Transaction or such earlier date as set forth above; provided,
          however, that if the value of the Transaction Consideration includes
          consideration the receipt of which is contingent upon the passage of
          time (other than the establishment of an escrow which shall be paid as
          described in the paragraph dealing with escrow above) or the
          occurrence of some future event or circumstance ("Contingent Value"),
          the portion of Blair's fee related to the Transaction Consideration
          attributable to such Contingent Value will be paid to Blair at the
          earlier of (x) the date on which payment of such Contingent Value is
          due or (y) the time that such Contingent Value can be determined.

     3.   Expenses.  The Company will reimburse Blair for all out-of-pocket
          --------
          expenses (including fees and expenses of its counsel and any other
          independent experts retained by Blair) reasonably incurred by it in
          connection with its engagement hereunder.  Such reimbursement will be
          payable within 30 days after submission by Blair of statements to the
          Company.
<PAGE>

                                      -5-

     4.   Indemnification.  Blair and the Company have entered into a separate
          ---------------
          indemnity agreement, dated the date hereof (the "Indemnity
          Agreement"), providing among other things for the indemnification of
          Blair by the Company in connection with Losses and Expenses (as
          defined in the Indemnity Agreement) in connection with Blair's
          engagement hereunder.  The terms of the Indemnity Agreement are
          incorporated by reference into this letter agreement.

     5.   Termination.  Blair's engagement hereunder may be terminated by either
          -----------
          the Company or Blair, with or without cause, upon written notice to
          the other party; provided, however, that (a) no such termination will
          affect Blair's right to expense reimbursement under Section 3, the
          payment of any accrued and unpaid fees pursuant to Section 2, the
          indemnification contemplated by Section 4 or the Indemnity Agreement
          and (b) if the Company, directly or indirectly, consummates any
          Possible Transaction within twelve months following such termination
          with any party (i) which Blair has identified and contacted, (ii) in
          respect of which Blair has rendered advice, or (iii) with which the
          Company has directly or indirectly held discussions prior to such
          termination, then Blair will be entitled to the full amount of the fee
          contemplated by Section 2.

     6.   Governing Law; Jurisdiction; Waiver of Jury Trial. This letter
          -------------------------------------------------
          agreement and the Indemnity Agreement will be deemed made in Illinois
          and will be governed by the laws of the State of Illinois.  The
          Company irrevocably submits to the jurisdiction of any court of the
          State of Illinois or the United States District Court of the Northern
          District of the State of Illinois for the purpose of any suit, action
          or other proceeding arising out of this letter agreement or the
          Indemnity Agreement, or any of the agreements or transactions
          contemplated hereby, which is brought by or against the Company.  Each
          of the Company (and, to the extent permitted by law, on behalf of the
          Company's equity holders and creditors) and Blair hereby knowingly,
          voluntarily and irrevocably waives any right it may have to a trial by
          jury in respect of any claim based upon, arising out of or in
          connection with the Indemnity Agreement, this letter agreement and the
          transactions contemplated hereby (including, without limitation, any
          Possible Transaction).

     7.   No Rights in Equityholders, Creditors.  This letter agreement does not
          -------------------------------------
          create, and will not be construed as creating, rights enforceable by
          any person or entity not a party hereto, except those entitled thereto
          by virtue of the Indemnity Agreement.  The Company acknowledges and
          agrees that (i) Blair will act as an independent contractor and is
          being retained solely to assist the Company in its efforts to effect a
          Possible Transaction and that, other than as expressly stated in any
          Opinion, Blair is not being retained to advise the Company on, or to
          express any opinion as to, the wisdom, desirability or prudence of
          consummating a Possible Transaction, (ii) Blair is not and will not be
          construed as a fiduciary of the Company or any affiliate thereof and
          will have no duties or liabilities to the equityholders or creditors
          of the Company, any affiliate of the Company or any other person by
          virtue of this letter agreement and the retention of Blair hereunder,
          all of which duties and liabilities are hereby expressly waived and
          (iii) any Opinion or advice rendered by Blair does not constitute a
          recommendation to any equityholder that such equityholder might or
          should take in connection with the Possible Transaction.  Neither
          equityholders nor creditors of the Company are intended beneficiaries
          hereunder.
<PAGE>

                                      -6-

     8.   Blair; Other Advisors.  It is understood and agreed that Blair may,
          ---------------------
          from time to time, make a market in, have a long or short position in,
          buy and sell or otherwise effect transactions for customer accounts
          and for their own accounts in the securities of, or perform investment
          banking or other services for, the Company and other entities which
          are or may be the subject of the engagement contemplated by this
          letter agreement.  The Company confirms that it will rely on its own
          counsel, accountants and other similar expert advisors for legal,
          accounting, tax and other similar advice.

     9.   Other.  The Company agrees that it will not enter into an agreement
          -----
          with respect to a Possible Transaction involving a sale of all or
          substantially all of the Company's assets or operations, unless such
          agreement expressly provides for the unconditional assumption of the
          Company's obligations to Blair under this letter agreement and the
          Indemnity Agreement.  This letter agreement may not be modified or
          amended except in writing executed by the parties hereto.  This letter
          agreement, and any modification or amendment thereto, may be executed
          in counterparts, each of which will be deemed an original and all of
          which will constitute one and the same instrument.

If the foregoing correctly sets forth our agreement, please so indicate by
signing below and returning an executed copy to us.  We look forward to working
with you.

                                   Very truly yours,

                                   WILLIAM BLAIR & COMPANY, L.L.C.



                                   By: /s/ Kelly J. Martin                    .
                                      -----------------------------------------


ACCEPTED AND AGREED AS OF
THE DATE FIRST ABOVE WRITTEN

PLANVISTA CORPORATION



By: /s/ Phillip S. Dingle     .
    ---------------------------
<PAGE>

                             PlanVista Corporation
                                  PO Box 30098
                             Tampa, FL 33630-3098



                                 July 17, 2001



William Blair & Company,  L.L.C.
222 West Adams Street
Chicago IL 60606

Gentlemen:

In connection with your engagement by PlanVista Corporation (the "Company")
pursuant to the letter agreement of even date herewith (the "Engagement
Letter"), as the same may be modified or amended from time to time hereafter,
the Company hereby agrees to indemnify and hold harmless William Blair &
Company, L.L.C. ("Blair") and each of the Other Indemnified Parties (as defined
below) to the fullest extent permitted by law, from and against any and all
losses, claims, damages, obligations, penalties, judgments, awards, costs,
disbursements and liabilities (including amounts paid in settlement)
(collectively, "Losses") and expenses (including, without limitation, all fees
and expenses of Blair's and each of the Other Indemnified Parties' counsel and
all of Blair's and each of the Other Indemnified Parties' reasonable travel and
other out-of-pocket expenses incurred at the Company's request or otherwise
incurred in connection with the investigation of any pending or threatened
claims or the preparation for, the defense of, or the furnishing of evidence in,
any pending or threatened litigation, investigation or proceedings, whether or
not Blair or any Other Indemnified Party is a party thereto) (collectively,
"Expenses") based upon, arising out of or in any way relating to (a) oral or
written information provided by the Company to Blair or any party to a Possible
Transaction (as defined in the Engagement Letter), (b) action by the Company or
action by Blair at the request of the Company or with the Company's consent, (c)
any Possible Transaction or any Opinion (as defined in the Engagement Letter) or
(d) Blair's engagement under the Engagement Letter; provided that the Company
will have no obligation to indemnify and hold harmless Blair or any of the Other
Indemnified Parties pursuant to this clause (d) in respect of any Losses or
Expenses which are finally judicially determined to have resulted primarily and
directly from the gross negligence or bad faith of Blair in fulfilling its
duties under the Engagement Letter.  Expenses will be reimbursed or advanced
when and as incurred promptly upon submission by Blair of statements to the
Company.  The Other Indemnified Parties will mean and include (i) Blair's
affiliates, (ii) the respective members, principals, partners, directors,
officers, agents and employees of and counsel to Blair and its affiliates, (iii)
each other person, if any, controlling Blair or any of its affiliates and (iv)
the successors, assigns, heirs and personal representatives of any of the
foregoing.

If any litigation, investigation or proceeding is commenced as to which Blair
proposes to demand indemnification, Blair will notify the Company with
reasonable promptness; provided, however, that any failure by Blair to notify
the Company will relieve the Company from its obligations hereunder only to the
extent the Company has been prejudiced by such failure or delay.  Blair will
have the right to retain counsel (and local counsel, if appropriate) of its own
choice to represent it, and the Company will pay the reasonable fees, expenses
and disbursements of such counsel.  The

<PAGE>

PlanVista                             -2-                          July 17, 2001

Company retains the right to participate in the defense of such litigation,
investigation or proceeding as to which Blair seeks indemnification through
counsel of the Company's choice (the cost of which will be paid by the Company)
and Blair will reasonably cooperate with such counsel and the Company
(including, to the extent possible and consistent with its own interests,
keeping the Company reasonably informed of such defense). The Company will be
liable for any settlement of any claim against Blair made with the Company's
written consent, which consent will not be unreasonably withheld.

If, for any reason, the foregoing indemnification is unavailable to Blair or any
of the Other Indemnified Parties or is insufficient to hold them harmless in
respect of any Losses or Expenses, then the Company will contribute to the
amount paid or payable by Blair or any of the Other Indemnified Parties as a
result of such Losses and Expenses in such proportion as is appropriate to
reflect the relative benefits (or anticipated benefits) to the Company and its
stockholders on the one hand and Blair and the Other Indemnified Parties on the
other hand from the Possible Transaction, or if such allocation is not permitted
by applicable law, then in such proportion as is appropriate to reflect not only
the relative benefits received by the Company and its stockholders on the one
hand and Blair and the Other Indemnified Parties on the other hand, but also the
relative fault of the Company, its directors, officers, employees, agents and
advisers (other than Blair) on the one hand and Blair and the Other Indemnified
Parties on the other hand, as well as any other relevant equitable
considerations.  The relative benefits received (or anticipated to be received)
by the Company and its stockholders on the one hand and by Blair and the Other
Indemnified Parties on the other hand will be deemed to be in the same
proportion as the Transaction Consideration (as defined in the Engagement
Letter) bears to the total fees paid to Blair pursuant to the Engagement Letter.
The relative fault of any party or other person will be determined by reference
to such party's or person's knowledge, access to information and opportunity to
prevent or correct any misstatement, omission, misconduct or breach of duty.  In
no event will the amount required to be contributed by Blair and the Other
Indemnified Parties hereunder exceed the total amount of fees paid to Blair
pursuant to the Engagement Letter.  You and we agree that it would not be just
and equitable if contribution were determined by pro rata allocation or by any
other method of allocation which does not take account of the equitable
considerations referred to above.

The reimbursement, indemnity and contribution obligations of the Company
hereunder will (i) be in addition to any liability which the Company may
otherwise have, (ii) survive the completion or termination of Blair's engagement
under the Engagement Letter and (iii) shall be binding upon any successors and
assigns of the Company.

In the event that any litigation, investigation or proceeding relating to the
transaction contemplated by the Engagement Letter is commenced or threatened
against the Company, the Company will not settle any such pending or threatened
litigation, investigation or proceeding unless (i) Blair, by name, and the Other
Indemnified Parties, by description, are included in any release or settlement
agreement, whether or not Blair and the Other Indemnified Parties are named as
defendants in such litigation or proceeding, (ii) Blair and the Other
Indemnified Parties are unconditionally released from all claims and liabilities
asserted or which could have been asserted in such litigation, investigation or
proceeding and (iii) there is no statement in any such release or settlement
agreement as to an admission of fault, culpability or failure to act by or on
behalf of Blair or the Other Indemnified Parties.

This Indemnity Agreement will be deemed made in Illinois.  The validity and
interpretation of this Indemnity Agreement will be governed by, and construed
and enforced in accordance with, the laws of the State of Illinois applicable to
agreements made and to be fully performed therein

<PAGE>

PlanVista                             -3-                          July 17, 2001

(excluding the conflicts of laws rules). The Company irrevocably submits to the
jurisdiction of any court of the State of Illinois or the United States District
Court of the Northern District of the State of Illinois for the purpose of any
suit, action or other proceeding arising out of this Indemnity Agreement which
is brought by or against the Company. Each of the Company (and, to the extent
permitted by law, on behalf of the Company's equity holders and creditors) and
Blair hereby knowingly, voluntarily and irrevocably waives any right it may have
to a trial by jury in respect of any claim based upon, arising out of or in
connection with this Indemnity Agreement.

This Indemnity Agreement may not be modified or amended except in writing
executed by the parties hereto.  This Indemnity Agreement, and any modification
or amendment thereto, may be executed in counterparts, each of which will be
deemed an original and all of which will constitute one and the same instrument.


                                             Very truly yours,

                                             PLAN VISTA CORPORATION

                                             By:           /s/ Phillip S. Dingle
                                                --------------------------------
                                                Name: Phillip S. Dingle
                                                Title: CEO


Agreed and accepted as of
the date above.

WILLIAM BLAIR & COMPANY, L.L.C.


By:                   /s/ Kelly J. Martin
   --------------------------------------
   Name: Kelly J. Martin
   Title: Principal