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An LS1 swap, If no corners are cut and you want everything to look nice, will run a little under 10 grand. It can be done cheaper, but it wont looks as pretty
you're gonna need the motor and trans, new motor mounts, new trans crossmember, I think a new driveshaft, new wiring harness (or have the old one modified to all hell), if you use an f-body LS1 you're gonna have to notch the crossmember or get a new K-member, you'll need new shocks and springs at least for the front of your car (LS1 will shave some weight and the nose will raise up), and then there is a ton of little stuff that you'll need or want and it all adds up pretty fast