On my '83 W123, it cost about US $800 (included new front shocks) to have this done. I consider that a lot of money, however, at that point the car was about 14 years old and had about 215,000 mi. on it so I figured I had certainly gotten my money's worth.
My advice: If you pay someone to do it, take it to someone you trust. Would you be surprised to know that a dealer technician (or technicians) left off a few parts causing odd (dangerous?) steering behavior? That was the last time my M-Bs have been serviced at a dealership - I've subsequently found an independent that is a gem and does the stuff I don't have the tools or expertise to do.