I'm out of warranty and am about to cross the 50k mile mark... Been tuned for a couple thousand miles now. I'm not too worried about the cost to maintain as I have a great Indy mechanic. I would agree with what someone stated above that you should budget about $1,000 every 20k / 1 year of ownership....
Jet black e92 6mt 335xi:
18" BBS RGRs, KW v1, ESS Stage 2 flash, VRSF 7" FMIC, VRSF downpipes, JG Mods m-tech front, mtec V3 AEs, BMS OCC, hardwired valentine 1, p3cars gauge, amber delete, sport seats, factory oil cooler.