Look for an independent mechanictransmission guy.
Assuming that the major parts are reusable (case, drums, shafts, gears) you're only talking a few hundred for parts and labor. I had great results from an independent guy rebuilding my 'Cuda trans, after the local chain transmission ship completely screwed it up.
Unless labor on those GM trannies is a whole lot different from labor on Chrysler trannies, you should be able to knock a thou off that quote!
Jim
p.s.--If you rebuild it yourself, cleanliness and caution are the keys! Dent/scratch the valve body and you buy a new one. Open the valve body and watch ball bearings (valves) and springs go everywhere--and you're buying a new one. Personally, I'd leave it to the pros unless you have all of the following: the time to do a full rebuild without large breaks, an organized shop where you can do the rebuild yourself, mechanical ability to improvise stands and tools, and enough money to buy another trans if you screw this one up!