Actually, if I had the time and space for the auto repair hobby, I'd probably get another BMW and maintain it myself; The things aren't any harder to work on than a regular car. You do take a reliability hit, but eh, I could probably live with that. The parts are more expensive, but after market parts are a small fraction of the cost of dealer parts (or what a garage will charge you for parts,) so if you look around for deals, you don't end up paying that much more.
(the auto repair hobby has a lot to recommend itself; It's an easy $90/hr post-tax for doing something that is not very stressful at all.)
Still, in a situation where you are paying someone else to maintain the thing, if you aren't willing or able to pay for a new BMW, (which comes with free maintenance for a period) you probably should also avoid a used BMW. too. This is why used 7 series bmws go for so little.
I don't think I ever got the BMW out of the shop for under a grand. Part of that is the BMW has excellent breaks, and excellent breaks wear faster than mediocre breaks. (apparently the metal dust coming off the pads and rotors are actually an important way to vent heat.) and for some reason, replacing the pads and rotors on a bmw was north of a grand by itself. (It was $250 in parts to do it yourself, and maybe two hours of work.) so I think a lot of it is just "oh, he has a bmw, he must have money" Also, well, the BMW reliability just isn't up to the same standards as the Japanese cars, so you'd have little problems that sometimes required a tow.
I knew a guy who said "I like older cars because I can work on them". And he did. Every weekend. I vowed I would purposely never learn how to work on cars so that I would never be tempted get involved in such a tremendous time sink. The worst thing about the hobby is it tends to insert itself exactly when you don't want to do it.
So really, for any given car, if you work on it yourself, you shouldn't be spending much more time than what the shop would charge you for the same work, and, uh, like I said, $90/hr post-tax isn't something most of us sneeze at. (Of course, if you can sneeze at that, good for you!)
that said, right now I'm taking my vehicle to a professional. the thing is, sure, the car only needs something once every 6 months, if you don't count oil changes (which I usually take in, just 'cause it's worth twenty bucks to not deal with the oil) - the thing is, where I am now, maintaining a garage would cost me more than just paying to take my car in. So yeah, it doesn't always make sense.