Just to give you an idea on LT1 prices, I paid $1000 for my used (50,000 miles) engine close to two years ago.
My friend just bought two LT1's 3 months ago from a junk yard for $750 (yes 750). I don't know what the mileage was. This included the harness for both engines. Not to sure about the computer.
Look around if you want a LT1 and don't pay a high price, they can be bought.