How much is a full diagnostic work up going to be on my 2001 E320 with 250k miles? I have heard nightmares from others who took their car to PS MB for diagnostic only to end up with $500 bill. MB of Riverside was suggested as cheaper.

I spent $330 for a partial diagnosis of a rough idle. The diagnosis was a cam solenoid, had it subsequently repaired did not solve the issue. Local independent dealer ran a diagnostic analysis for free discovered a bad spark plug solved the problem that I've had for 2 years. Very disappointed

labor rates at any MB dealer are very high. not surprised duagnostic cost $500

Most dealerships are going to be more expensive for such things, in particular if its a very high milage car. If you call the service manager ask for an agreed upon price.