<PAGE>

                                                                   EXHIBIT 10.30

                       THIRD AMENDMENT TO CONTRACT OF SALE

        This THIRD AMENDMENT TO CONTRACT OF SALE (this "Amendment") is made and
entered into effective as of the ____ day of June, 2004 (the "Effective Date"),
by and among VORTISCH HOLDINGS, L.P., a Texas limited partnership ("Seller"),
CANTEX REALTIES, INC., a Texas corporation ("Cantex"), and REALTY AMERICA GROUP
(4245 CENTRAL), LP, a Texas limited partnership ("Purchaser").

                             PRELIMINARY STATEMENTS:

        The following preliminary statements are a material part of this
Amendment:

        A.      Seller, Cantex and Realty America Group I, LP, as predecessor in
interest to Purchaser made and entered into that certain Contract of Sale, dated
effective April 16, 2004 (the "Original Contract"), with respect to certain real
property located on that certain tract or parcel of land situated in the City of
Dallas, Dallas County, Texas, which is more particularly described in the
Contract (the "Property"); as amended by that certain First Amendment to
Contract of Sale (the "First Amendment"); as amended by that certain Second
Amendment to Contract of Sale (the "Second Amendment")(the Contract, the First
Amendment and the Second Amendment are hereinafter collectively referred to as
the "Contract").

        B.      Cantex is only a party to this Amendment and the Contract as is
necessary for Purchaser to enforce certain representations and warranties
provided by Cantex to Purchaser under the Contract.

        C.      Seller, Cantex, and Purchaser desire to amend the Contract as
set forth below.

                                   AGREEMENTS:

        NOW THEREFORE, in consideration of the agreements to sell and purchase
the Property and the mutual covenants and agreements contained in this Amendment
and in the Contract, and other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, Seller, and Purchaser hereby agree as
follows:

1.      EXTENSION OF INSPECTION PERIOD. Pursuant to the terms of the Contract
        and the Second Amendment, the Inspection Period shall expire on Friday,
        June 4, 2004. However, Seller, Cantex and Purchaser hereby agree to
        extend the Inspection Period, including, but not limited to, the right
        to review the updated survey and title commitment, under the Contract to
        Monday, June 21, 2004.

2.      ADDITIONAL EARNEST MONEY DEPOSIT. As consideration for the additional
        extension of the Inspection Period, Purchaser hereby agrees that if, as
        and when this Amendment is fully executed, Purchaser shall, by Friday,
        June 11, 2004, deposit an additional sum of Seventy Five Thousand and
        No/100s Dollars ($75,000.00) (the "Extension Deposit") with the Title
        Company. The Extension Deposit shall become part of the original Earnest
        Money deposit, and shall be fully refundable until the expiration of the
        Inspection Period.

<PAGE>

        In the event the Extension Deposit is not made by 5:00 p.m. (C.S.T.), on
        Friday, June 11, 2004, Purchaser shall be in default of the Contract,
        and shall forfeit the $25,000.00 Earnest Money Deposit made pursuant to
        the Contract.

3.      CLOSING DATE. In the event the Contract is not terminated prior to the
        expiration of the Inspection Period, Purchaser and Seller hereby agree
        that the Closing Date under the Contract shall be Monday, July 19, 2004.

4.      TERMINATION OF CONTRACT. In the event Seller, Cantex and Purchaser have
        not executed, and delivered to the other parties, this Amendment prior
        to the expiration of the Inspection Period set forth in the Contract,
        the Contract shall terminate, and be of no further force or effect, and
        the Earnest Money heretofore deposited by Purchaser shall be immediately
        returned to Purchaser. Such termination shall take effect without any
        further documentation on the part of Seller, Cantex or Purchaser.

5.      CAPITALIZED TERMS. Capitalized terms used but not defined in this
        Amendment shall have the same meaning as those in the Contract, unless
        otherwise noted herein.

6.      RATIFICATION OF CONTRACT. Except as specifically modified by this
        Amendment, all of the other terms and provisions of the Contract shall
        remain in full force and effect, and are hereby ratified and confirmed
        by Seller, Cantex and Purchaser. Notwithstanding the foregoing, in the
        event there is any conflict between the terms and provisions of the
        Contract and this Amendment, the terms and provisions of this Amendment
        shall control.

7.      REPRESENTATIONS AND WARRANTIES. Seller, Cantex, and Purchaser represent
        and warrant to each other respectively that they have the requisite
        power and authority to enter into this Amendment; that all necessary and
        appropriate approvals, authorizations and other steps have been taken to
        effect the legality of this Amendment; that the signatories executing
        this Amendment are authorized to do so on behalf of Seller, Original
        Purchaser and Purchaser; and that this Amendment is valid and binding
        upon and enforceable against Seller, Cantex, and Purchaser.

8.      COUNTERPARTS. This Amendment may be executed in any number of
        counterparts, each of which shall be deemed an original. Facsimile
        copies of the signature pages to this Amendment shall be deemed to be
        originals for all purposes of this Amendment.

9.      FINAL AGREEMENT. This Amendment and the Contract cover in full, each and
        every final agreement of every kind or nature whatsoever between Seller,
        Cantex, and Purchaser concerning the Property, and all preliminary
        negotiations and agreements whatsoever of every kind or nature are
        merged into this Amendment and the Contract. This Amendment and the
        Contract cannot be changed or modified in any manner other than by
        written amendment or modification executed by Seller, Cantex and
        Purchaser.

10.     SUCCESSORS AND ASSIGNS. This Amendment is binding upon and inures to the
        benefit of Seller, Cantex and Purchaser and their respective successors
        and assigns.

<PAGE>

        IN WITNESS WHEREOF, Seller, Cantex, and Purchaser have caused this
Amendment to be duly executed as of the Effective Date.

                                SELLER:

                                VORTISCH HOLDINGS, L.P.,
                                a Texas limited partnership

                                By: VORTISCH INVESTMENTS, INC.,
                                    a Delaware corporation
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Hermann Vortisch
                                             President

                                    Date of Signature: June ____, 2004

                                PURCHASER:

                                REALTY AMERICA GROUP (4245 CENTRAL), LP,
                                a Texas limited partnership

                                By: REALTY AMERICA GROUP INVESTMENTS, LLC,
                                    a Texas limited liability company
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Webb M. Sowden, III
                                             Member

                                    Date of Signature: June  ____, 2004

                                CANTEX:

                                CANTEX REALTIES, INC.,
                                a Texas corporation


                                By:
                                      ------------------------------------------
                                Name:
                                      ------------------------------------------
                                Its:
                                      ------------------------------------------

                                Date of Signature: June  ____, 2004