Used BMWs may lure you in with their low asking prices, but maintenance and repairs can quickly make that shoot up.
My experience working on BMWs has been pretty bad. Recently I tried to help out a friend of my little brother with his 325i that had a bad thermostat. It turns out that the automatic transmission versions have an additional fan, a mechanical fan that gets in the way of thermostat replacement and is not straightforward to remove. I spent a few hours trying to get it out, but there was one bolt that I couldn't get to, and I couldn't remove the fan, so I put it back together and gave up. He had to get it replaced at a mechanic, and then later it blew a head gasket(probably related to previous overheating).
Previously, a friend and former coworker had bought a 325i of the same generation as the one in the story above, this time with a manual transmission. It had a blown head gasket that wouldn't allow him to leave the radiator cap on when cold, so he had to warm the engine up then put it on. I had never driven an inline 6 car before so I wanted to try it out. Battery was dead of course, so we went to bump start it. I went to shift into gear and it didn't do anything! Of course the moment I get in the car the shift linkage disconnects.
Even less recently, I had a 325i come into my workplace that was all sludged up at 60,000 miles. I used to want one of these little inline 6 BMWs, but these experiences have made me re think that decision. Unfortunately I can't convince my little brother otherwise, he still wants one.