Brake Rotors grinding down service charge to much.....? on 2002 Mercedes-Benz C32 AMG

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,

Sounds about right to me, if they fixed it...
Would've been more where I live..
Thank you Superbob, I appreciate the response. That is good to know that I did not get ripped off.
1 more answer , 1 more comment
the price was OK if it fixed the problem.
It would have been $300.00 at Davis Automotive
Naperville Il
By the way we can do the COVERED warranty repairs
Thank you for your reply. Are you saying that you would of fix this for me under my warrenty that carmax did not?