As stated in the previous replies, your cost basis is $3,000. I can't be any more clear about it. Since your cost basis is $3,000, enter $3,000 as the cost basis in TurboTax.
The proceeds are $2,250, so you enter $2,250 as the proceeds.
You do not enter the gain (profit) or loss. TurboTax calculates the gain or loss after you enter the cost basis and proceeds. You do not enter $750 anywhere. TurboTax calculates it.
