2006 STS 4 AWD 3.6
From my experiences with my STS and owning several BMWs in the past is these vehicles are NOT ridiculously expensive to repair. I'll say that again. NOT ridiculously expensive to repair.My advice is to avoid these money pits all together. The cost of regular repair on these cars is ridiculous.
Many electrical issues will start popping up given the age of these cars.
Now, that is IF you know where to buy inexpensive parts and you do your own repairs. I get it most folks do not do their own repairs. I've farmed out plently work because of the weather and just plain laziness. So in that regard, my rule of thumb is to never ever, ever, ever, EVER go back to the Stealship for repairs! They'll tear your heart out and eat it ! Lol ! One exception is if your car is under Warranty.
The other option for mechanically work is shop around for a good, inexpensive mechanic ! You "may" have to venture into the sleazy part of town BUT there are good, decent, inexpensive mechanics there. Just because they are poor does NOT mean they suck as human beings.
For parts, of course EBay is king and if you want to buy used check out..... www.Car-Part.com That is the Internet's resource for a massive amount of wrecking yards across the country. Familiarize yourself on how to Search for the least expensive and closest parts. I guarantee you save a shit load of $$$ in the process.
BMW has several websites that cater to BMWs only and the parts there are NOT much more expensive that any domestic brand.