Don't worry about those, all drilled discs will do this after a while. Whilst most techs would say they need changing, I have seen far worse and have had far worse on previous cars.
Not sure if your car is a PP, but if it is I can see where the massive price for replacement has come from. I am led to believe the std c63 discs will fit as they are the same size. This is what I have heard, so not 100% Sure.
If you did not want to spend the crazy price the PP discs are you could put normal ones on. Lets face it the PP discs are not that much better than normal if they are the same size and most people will not notice any difference driving on the road.
Even on track you can cook the PP ones!!
If I knew what I know now I would have bought a standard C63 and fitted a LSD as this is the only reason I bought the PP.
The suspension is rubbish and for not much more than the price you were quoted for the brake change you can buy a AP racing brake kit.
Try cooking those on track.!!