parts and labor prices are greatly over-exaggerated by people who dont own BMWs or ignorant owners.

as far as info and maintenance, it really depends on the model and year. 1997 and up youre starting to get into a more complicated car with more expensive parts and maintenance. but as it will be newer it probably wont need as much of either. either way the baby six motor is shared with the 3 series of those years, so 97+ 528 is same motor as 97+ 328, same goes for the older 525/325. so parts wont be much different than the 3. and the 535s have an old style single cam motor thats cheap to maintain. however, the v8s will become quite a bit more expensive.