Call a salvage yard, get a used transmission for half of what the rebuilt one cost. Get one with a warranty.

You can replace a transmission in an afternoon if you have the right tools. All you have to do is pull the axles, shift and clutch linkage, and then there's like 8 bolts that hold it to the engine. The clutch stays bolted to the flywheel, and you can transplant your throwout bearing. The transmission holds 2 quarts. You'll need a air chisel with a punch attachment to knock the dowel pin out of the shifter rod on the shift linkage or you'll be cursing for hours. I posted about that years ago.

If you shop around in the For Sale section, you will probably find a tranny for even less. Maybe like $200-$250. Probably won't have a warranty, but you know...