I wouldn't go to the dealer for something like that, a regular old machine shop is fine. I think I paid about $80 for my valve job and resurfacing ('85 190E 2.3 8V). Might of taken them an hour to do it. A typical valve should be $5-10, guides about the same (installing the guides is where they get you), and springs less than that, but since it's a MB who knows. I had to buy seals too, another $20 or so. My head gasket is what really surprised me, $100!
My BMW needed a head gasket, but they wanted $240 for that sucker, so I never did buy one.

Shop around, the best price I found was a local place that only does heads.