I've been looking into older Audi's and BMW's but am scared of the potential high cost maintenance. How have yours been reliability wise?
If they aren't well maintained, they can have a lot of issues. Most of the ones I got were cheap because the previous owner had problems with them, and some were pretty serious. If you don't plan to do the work yourself, or buy a well maintained model from an audi/bmw enthusiast, it can end up costing a lot of money.
On the other hand, if you fix one up and replace all the stuff that commonly goes out, it'll be super reliable and drive like a dream. I spent about a grand buying parts for the e46 when I first got it. But after the first year, I ran out of things to fix. I put less than $200 worth of parts into it last year, zero so far this year. Some of those were optional repairs too.
I think bmw's are easier to work on than audi's though. The way they disassemble makes more sense to me.