Another expense is replacement of the rear subframe bushings, unless they've been replaced. Symptom is a very rough ride in the rear.
Do you have firet-hand knowledge of this indie?
Mike Miller, a BMW tech editor, recommends only BMW factory rebuilt transmissions. Might want to get a quote from the indie for one of those.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.