I got my 6.0l Ro's remap done at Rapid GB for £250 because he was doing a deal at that time. But i think his normal price in £499 give them a call 01933 272087
ask Mark at Rapid what he's charging these days for a remap, might be a bit cheaper. He did my 04 CV8 couple of years back and it outperformed a 06 model CV8 Wortec tuned car at a rolling road day so worth a call to check.