Just take the head. The existing seats will be ground. They may determine some valves and guides may need changed as well. Get a price estimate from them.

Valve jobs used to be cheap here. Perhaps they still are where you live. You could ask any local repair shop that services mercedes where they send their mercedes cylinder heads for reconditioning and the average charge they pay. That increases the chance the place you take the head will do the job properly.

Before taking the head in open some valves and look to see if there is a lot of carbon buildup on the seats and valve faces. Carbon alone in large amounts could stop the valves from sealing.

Do not spend more money than the car is worth. Old mercedes repair shops used to do the valve jobs themselves years ago.