I don't know exactly, but when I bought parts for my wife's Mazda6 (brakes, etc.) they weren't outrageously priced (I want to say I spent around $250-300 for 4 new rotors and 2 sets of pads) that I installed myself.

a quick search for A6 rotors yields a price of 150/rotor for the quattro($600 for 4) + pads ($65/set for the cheapies) brings the total to $735.

http://www.nextag.com/audi-a6-brake-rotors/search-html

http://www.racepages.com/products/?D...6884&Nty=1

Even if you go with the nice Rotora drilled/slotted rotors on the MS6, they are $100/rotor, so 33% less for a high performance part.
http://www.streetunit.com/Rotora_Rea...168.45074c.htm

 

Well here's a comparison for a Boxster:

Front brake pads: $91
Rear brake pads: $122
Front brake rotors: $252
Rear brake rotors $278

All told: $743

With labor @ $125/hr, that would easily be a $1000 job.