I toyed with the idea of replacing mine to cure a weird problem, and my sources show that the price is probably a little high.
Fastlane shows them to be less than $130, even lower than the list price, which is around $150, still $20 lower than the quote you got.
Dealer parts quotes are almost always higher than other sources, so unless I am buying a hard-to-obtain trim piece or MB antifreeze, I stay away from the MB parts counter...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car