It's going to vary alot. There are some independent shops that charge less than going to a dealer. That can be a tradeoff though. Some are real good, others not so good. The same can be said for the dealer of course, but at least the dealer has a better chance of having personel well trained in the product.
The hourly rate is what greatly effects the end cost.
That being said, these days it's kind of a murky thing as far as what a "tune up" consists of. There's not much to adjust on the engine, mostly replacing spark plugs and the fuel and air filters. maybe checking the computer for trouble codes, stuff like that.
Once you start approaching this amount of miles you have to make sure the transmission fluid and filter were replaced somewhere in the last 30,000 miles or so, and Benz is kinda picky on replacing the coolant and brake fluid every so often.
So, if you wnated to make sure everything on the car is in spec, you'd probably want to get what MB calls the "150,000 mile service". On the low side, assuming just replacing the maintenance stuff (no extra work needed like brake pads and rotors or tires, extra stuff like that) probably be looking at $200. That's if you find a good independent who works fairly cheap (up to you to find such a person), or at a dealership may be up around $400-$500. That's for everything I just mentioned-oil change, trans service, spark plugs, fuel filter, air filter, cabin filter, all that stuff, parts and labor.