The A6's don't have the turbo failures that the S4's did because the engine bay is much larger and allows for better cooling. With that said, it still won't have any warranty, and will require more maint (synthetic oil, more expensive filters timing belt service if it wasn't done already etc).
I would look into the A4 range for that price, and the GTI/GLI from VW. With any used car, you should expect to have to take care of a few things (change all of the fluids, plugs, filters etc) to get it 100%, and should have a few bucks tucked away for some repairs.
No German car will have Honda reliability, but my wife and I's last 3 VW's (bought new though) have 33k miles with 0 service visits.