in all honesty, probably about the same as maintaining a late model Asian car; provided you have a mech you know you can trust and not have to rely on the dealers.
Parts abound on the internet for surprisingly about the same as any ole' car; or say 15% more due to import duty...
Technically a car is a car; be it a bimmer or the lowly tuk-tuk. All the hype that u see on commercial, read in the papers, or tech jargon that techs use are just there to make ur car"special" and sophisticated in some way... and that idea forms the basis for the dealers to squeeze that extra $ off ur wallet just because...(*whispering), it's a bimmer. hehehehe
Case in point: BMW uses "VANOS"... HONDA's version is "VTEC". In essence, the theory, the tech, and the engineering is the same.
...kinda like saying if you are too stuck up on a car because of the "roundel", and you need to run to the dealer to keep it running... YOU WILL BE SCREWED!