How much does a transmission for an 96 Audi A4 2.8 FWD cost?!?!?

im looking for a car for my 16th birthday in 12 days...and i can get an 96 Audi A4 2.8 FWD for a decent price. but it needs a transmission. i have a grandpa who's a mechanic and owns a shop plus my dad is amazing with cars.. all i need to know is how much a transmission would cost so i know if i should buy this car...please help!