If MB parts prices make you cringe Jag parts prices will give you heart burn!
Evap core on a W140 isn't as big of a deal as people make it out to be, a shop I know in NJ will do it for just over $2k. Or you can do it yourself over a long weekend for like $400.
Any high end car will have potential expensive issues that is just the nature of the beast. These cars cost $70k+ new. Most people that I know that have bought cars such as this new do not bat an eye at $3k a year maintaince or a $5k bill once in awhile. They just drop it off at the dealer or the shop they use and let them do what they want.
Buy what you want, none of these cars are a Camry or Sable so budget accordingly.
I still vote for a 1997 XJ6 or S420/320. W210's in general are pretty user friendly to drive and take care of.