On our 1991 Vette it was $1500 and they never got it right...we even had it done at Amaco. They had to rebuild part of it again a second time because it was done incorrectly the first time.
Make sure you get someone who knows how to rebuild a vette transmission. We thought we did, but he really had no idea. Very frustrating! We no longer have that car, we traded it in.
Good luck! Also, it would be worth it to get an extended warranty, might cost you $700 or so, but it would be worth it if you have the $$