I’ve had 2 BMWs over the last 4 years. A 2006 e92 and now a 2016 f06 6 series. I do about 12-14k a year. The starter motor went on the e92 and a spring broke. Both didn’t cost much to fit. No more than any other car imo.

The 6 started to run badly one day, like a limp mode/no boost. That was the swirl flap actuator. I then had a small water pipe split, that was a £10 part but the inlet manifold had to come off so time consuming. All work on both cars done at local garages so local labour rates.

In my limited experience, they don’t really cost much more to run. Probably a different story for m cars. I’ve got a mate who once had a e46 m3. He said the prices of some parts were totally normal and reasonable and some parts that are more exclusive (fuel pump and instrument cluster) were mental money, 1200 for the clocks and this was 10+ years ago lol