Medical bankruptcy cases tend to be less expensive than those filed primarily for other debt reasons. While a medical bankruptcy is really just a regular Chapter 7 or Chapter 13 case, they tend to involve fewer assets and lower income households. A bankruptcy attorney will give you a fair quote based on the time and expertise necessary to successfully complete your case.
There is a natural empathy for people that need to file bankruptcy because of medical bills and therefore some of the lowest priced cases tend to be those caused by medical bills.
When you think about the total cost, consider that about the first $400 or more is not for attorney fees, but for court costs (currently at $338 for Chapter 7) and bankruptcy specific credit reports, which can be upwards of $40 each.  If, for example, an attorney quoted you $1,600 for a medical bankruptcy, the actual attorney fees would really be around $1,200.  Prices do vary depending on the number of creditors and the amount that you owe, your income, the value of your assets and generally how much time will be necessary to properly file your case.
If you have an ongoing medical problem, then Chapter 13 may be a much better option that you should discuss with your attorney.