I have a 93' 325 with a "dying" auto tranny. I took my car to a transmission shop today for an tranny oil/filter/gasket change and they stated it had an inch thick of metal particles on the pan. They recommended rebuilding it between $1800-$2000 and I said yeah right!

They said I need to rebuilt it and do not recommend just replacing with a used tranny.
My questions to you: Should I just buy a used auto tranny ($700)and hope it won't have the same problem? Should I consider another type of tranny, if so what kind? (Not sure what model types of tranny works with a 93') Maybe an auto to manual swap? (What's the cost?)
Any recommendations and suggestions from experience is greatly appreciated in advance! Thanks!