I found my price comparason spreadsheet I made up (no jokes about tight scotsmen please)
the dollar exchange rate and shipping will have changed for the worse because the pound has dropped, but you get the idea....
Price (pr) Shipping Duty VAT TOTAL
Kunzmann 1454 12.54 0 0.00 1466.54
ECS 1000 91.48 45 227.30 1363.78
Inchcape 1492.56 0 0.00 1492.56
car parts.com 980 100 44.1 196.00 1320.10
Eurocarparts 1357.08 0 0 0.00 1357.08
car parts for less 1292.48 0 0 0.00 1292.48
Racing Brake 792 127.64 35.64 191.06 1146.34
Racing Brake (Amazon) 659 127 29.655 163.13 978.79
mymercedesparts.com 980.44 44.1198 204.91 1229.47
Evosport 917 91.48 41.265 209.95 1259.69
Note you can buy the racing brake discs from amazon and they're cheaper!
RacingBrake 2141-381 Open Slotted Finish Front Brake Rotor for C63 AMG / E63 AMG - Pair : Amazon.com : Automotive
Also note if you buy in the UK, car parts for less are better than Eurocarparts although they are the same outfit.
Not sure if there is any impact on anyone's warranty using non-OEM etc.
Also, I fitted the new discs and pads myself, really easy to do.