A lot depends on what you want out of it, how much you want to spend, what shape the rest of the car is in and and how much you can do yourself. If it's a keeper get a factory reman unit. If you can do work yourself, get a used one at a pick and pull for $100 or so. If it was me, I'd buy a driveable wreck, so at least I could check the tranny condition, and just swap.
You should be ably to find one under $500.