I do not even know what a decent price is anymore. It all depends on how whacked your tranny is. A buddy of mine spent $2,000 about four years ago but his tranny was in reasonably good condition. It was a 400 and all the usual stuff was done to it. The converter was reused and so was the valve body. I have heard you can spend $4,000 and more on these vintage tranny's. Good luck. 

Rebuilds always depend what you are looking to achieve from it. If you are looking for a basic rebuild, you can get a nice one done for around $1000.00 with a good street shift kit. But the sky is the limit. Rebuild kits range from 300hp units, beyond 2000 hp units which start at $1500 just for the parts. I have no idea where youre located, but reputable transmission shops are pretty much the same price across the board. Check who does transmissions for drag racers in your area, and youll find the shop that should do the work for you. Hope all works out well for you.
As a side note, I purchased a new 700 R4 TCI Streetfighter trans from Jegs and it cost $3800.00 Cdn by the time I landed home, and I picked it up in the US. So gauge appropriately. Cheers.