I agree with my colleagues. Your question is really a legal one. Go to the bank that you routinely do your banking with, and see how much of a mortgage you can qualify for. If you are in a position to do so, and have been prequalified with your lender/bank, then you can bid at auction.
Another alternative would be to start looking at other homes now, and if possible, attempt to recoup your loses from the owner of the home that you entered into a lease w/option to purchase agreement. Of course with the assistance of an attorney.
Best of luck to you.