Dont know sounds that way, I was looking for a used A4 not A6's. I ended up buying a brand new '09 but that would be quite a bit more expensive than 5k. The reason I bought brand new is I heard maintaince is quite expensive on these cars.
I worked at an Audi/VW dealership and have had 2 friends buy A4's. Both bought used ones at over 75k and both regret it. Both have dumped over 2k in maintenance only on the cars in one year, yet one of my friends does the work himself so he cuts the labor out of it (but still spent over 2k in just replacement parts.)
So yes, they can be expensive. But what car isn't?