i have just been quoted £250 to have a side skirt painted (already in primer as R32 version) and the rear valance smoothed down and sprayed - the same was as digger leaving part of it black. was about to start a post to see if that was a good price or not until i read this thread, still wondering now to be honest
I had my rear valance smoothed and painted leaving the lower portion original. Cost me £120 and was top noch.
To be fair they have to flat it, then plastic primer, then two-pack primer to make sure it's an even surface all before the base coat and then the lacquer, materials and labour £100 is fair IMO...