Before you go to a lot of time and effort trying to come up with a basis to report, you might just try entering into TurboTax the sale with $0 basis. Assuming you were a "child" over 1 year ago the the holding period is "long term" and you may find that entering the sale results in no increase in taxes. That's because if you are in the lowest two tax brackets long term capital gain is taxed a 0%. (Even if you're not in the lowest two tax brackets this probably would be taxed at the 15% long term capital gains rate.)
If your tax liability doesn't change at all or changes a very small amount you might just decide to leave that basis at $0.
Tom Young
