We would do this job for about $500-$550 depending on the pump and belt. I prefer the OE rebuilt pump, but have used the Graf and the Laso and both pumps work very well.
Good luck. PS, If you don't have the tools, don't even think about it on a 104 engine. The special 6mm allen sockets are a killer.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS