Brake Rotors grinding down service charge to much.....?

What is your question?

I just paid $345.00 service charge at carmax of Napperville,IL where I bought my C320 AMG 4 door sedan yesterday (2-21-2011) to grind down all 4 rotors and the charge of $345.00 was 4.7 hours of labor only. Does that sound right? Not sure if I got a bargin are was ripped off. I took it in thinking that the thumping sound the brakes where making was becuase of the abs not working right, I took it for a test drive with their mechanic and found out that it was the rotors had some rust on them from me not driving my car enough. Of course none of this was covered on my 7 year Maxcare warrenty. Just wondering if the price is right or wrong. thanks in advance, james