Here's the sad part; the '06 330i is one of the most reliable BMW's on the roads right now, and one that requires considerably less maintenance than others.
My '06 330i was pretty low maintenance, aside from routine stuff. That's the other thing. You really need to know what you're getting yourself into, before buying a used premium European auto. Us BMW rats will tell you that most of that stuff is pretty customary.
Now that you've been properly hazed by your car, welcome to the extended-warranty-is-worth-every-penny club.
2017 Mk7 GTI
2015 f80 M3
2013 f30 335i M-sport
2012 e92 M3 ZCP