My 300SEL has one pump. Some of the 103 equipped cars have 2 - not sure about yours.
Pump is $150-$300, depending on where you buy it. I can easily see this getting billed out as a 2 hr. job. $150 to $200 labor depending on where you live, so you could be looking at $300 to $500 unless you hire a shade tree type.
As was mentioned above, this is not too tough of a diyer job. Helps to back the car up on ramps - extra room to work.