How reliable are Audi's in general?

How reliable are 2000 S4's?

How expensive are Audi replacement/aftermarket parts?

I have a few cars/trucks but am looking to trade my BMW off because it is broken down almost as much as it is on the road. The damn car has almost turned me off to Germany cars all together. I found a 2000 S4 6 speed with 61000 miles for $20,995 and they would give me what I owe on my BMW. The $400+ per month payment is a little steep, is it really worth the expense? I want something that is fun to drive daily and can haul my golf bags and the family.

Sorry for all the questions...

Thanks