I just replaced my trans by myself this past November with some help and pointers from guys on this site. My trans was slipping and I got a price of over $2400 to rebuild mine from Aamco. I went the junk yard route and found a trans with half of the miles I had on my failing trans.
Quick summary:
Used trans...$475 with 67k miles
Fluid and filter and a few misc parts...$100
I already put 16k miles on it in 8 months
No problems at all