Some BMWs and Audis have more problems than others. You need to research it on ConsumerReports. You can have a 3-series from 2004 be great and 5-series from 2004 be a total POS.
Anyway, do you do your own repairs? It cuts down on maintenance costs. But, German parts cost a lot. When I had a BMW, I bought most of my parts from Bavarian Auto or BMP. Check out www.bavauto.com or www.bmpdesign.com for parts prices. That will give you a ballpark figure on what regular maintenance parts that wear down will cost. Radiator. Hoses. Brakes. Clutch. Tie rod ends. Bushings.
And if you end up with a BMW like mine, you will be driving around with a box of fuses and tail-light bulbs.
that's a LOT of maintenance.