transmission advice

I'm looking for some advice on a cruddy situation that just became cruddier. I drive a 1990 Silverado, 2WD, ext cab, long box, 345k miles, good engine, rebuilt transmission w/20k on it. I just lost 3rd gear on the transmission and the warranty has long since expired. I took it to a transmission shop so they could tell me what I already know, i.e. that the only option is a rebuild at $1,000+ warrantied. I'd say with a good transmission, this vehicle is worth about $1,000 in my market. Are they any *practical* options for a guy with a vehicle like this? I know a lot of guys who like to work on cars, but transmissions seem to be another tier of knowledge.

I have an 88. This has the same trans 700r4. Mine did the same thing. I went to a salvage yard and got a trans for almost nothing and installed it myself. Not hard. 6 bellhousing bolts, three torque converter bolts, 4 crossmember bolts, 1 tranny mount bolt, 4 bolts on the yoke of the rear end to drop the driveshaft, 2 electrical plugs and 2 tranny lines. I have changed mine twice, got it down to under 3 hours.