A March 2008 thread on the http://mbca.cartama.net/ forum indicates the harness can be purchased for about $500. You should also check with Phil here at Fastlane.

Although I didn't have to R&R my harness there was a time I thought I might have to do it and read many posts regarding the diy. It appears to require patience and a long afternoon, but is not technically difficult or requiring special tools.

Bob
PS R&Ring a Benz wiring harness gives new meaning to "Plug & play".