welcome to BC
Sounds like youre in the same boat i was with my cars, only i never had a need to replace a tranny and mine are very easy to locate with the N/A engine.
First, these things run forever as long as they are properly maintained. never an engine failure issue unless regular matienance is not done. I learned that the hard way with my 1992 SE.
timing chain broke, not fun.
heres the thing you wanna look into if youre thinking about if its worth fixing the car...
1. is it owned or a bank loan?
2. if you own it, and evvvvverything else is solid, then fix the car and find that transmission you need.
I had asked myself the same thing a few weeks back with my 2001 and i own that one and LOVE it now that it is maintained and restored. it was a project car to have and somewhat low miles. these cars willlll run forever if you want. it started with brake rotors to a presure seloniod in the transmission a week or 2 ago. ive put some $ out for my 01 and it runs great now.
see if its worth keeping or if you can get in another bonne for around the same price, check the for sale part of BC for a car that might be for sale. no one here is gonna sell a bad car im sure.