Used Audi's and maintenance costs?

Out of all the cars that I have been looking at recently to replace my wife's current car I really like the Audi A6 Wagon. I would like to find one that is 06-08 for a decent price. I have always been told that Audi's are expensive to have work done on and I'm just trying to see if that is actually true and if so how much? We have an older 2002 Protege 5 and I really like wagon's as we are expecting our first child in April so I need the trunk room. I don't care for the Subaru's larger wagon and the WRX is just too small and I just haven't seen any others that I really like. The only thing that really gets me excited is the A6 wagon but I don't really want big repair bills either.