If you absolutely positively need to buy Mercedes parts from a dealer and you don't have a wholesale account with you local dealer then check with Duval Motorsports. They sell MB parts for much less than MSRP.
http://www.trademotion.com/partlocator/index.cfm?siteid=213951&catalogid=0

The first part number that M.B.DOC gave the part number for is $420.