It depends on the type of work being done. The basic air conditioning system, for example, is essentially the same as the typical US car. The climate control system, however, is very "Mercedes." And the 300D is special in two ways. Not only is it a Mercedes, it's also a diesel.
To get your air conditioning fixed, I recommend you find a mechanic with lots of kids. You are going to have to give $800-1000 worth of music lessons, assuming that the compressor is the only problem.