Answer
Being as that it is a mercedes benz, and gerbloke cars are always right at the top of being the most expensive to maintain and repair, and being that you are the only one that knows your area(cali/ny/tx??) a "ballpark" estimate is about the best you are going to get.most headgaskets are a job and a half to do depending on whether its a 4/6/or 8 cylinder(mb 10 or 12) and the average time to repair one is going to differentiate with each vehicle.assuming that yours is a 4cylinder (2.3) it should not take more than 6-10 hours to complete plus parts with an average labor rate of $75.00 and parts being around $200.00.good luck and hope this helps.