I bought my 2000 328i with 58,500 miles on it for $23K (includes interest on the loan). I have had problems with sensors on the car, but no issues with the tranny yet. The biggest issue is the history of the car and how the driver treated it before you. I've heard the horror stories too, but have yet to see a problem.
If you maintain the car well from this point on, and don't try to do a "running start" from the reverse gear, the tranny should be fine. Basically, don't compound any problems. That sounds like a pretty decent buy. Compare it to the blue book and then subtract accordingly if the owner hasn't replaced the following:
Camshaft position sensors ($240)
Oxygen sensors ($400)
Spark plugs ($24)
Air filter ($10)
Cost of oil change, if not recent ($40)
Brake pads (have a mechanic verify adequacy) ($60)
Tires (ditto on the mechanic) ($400) - don't forget to check the spare for use!!
Most importantly, and this is my personal opinion, if you've decided you want to purchase a BMW, and you know the approximate year and model, purchase a code-fault reader. It will be the best $150 you ever spent. You can diagnose a car right in the owner's driveway and find out what errors are stored in the computer... and deduct from the price accordingly.