I have not EVER recommended a valve job on a 104 engine with head gasket replacement. I have on the 103, same chasis, different engine. I have done over 100 of these head gaskets and the only valve job was done to a car that was overheated.
With that out of the way, I think the job can be done for $800-$1,000.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS