Many parts stores will do an OBD scan for free. It might find your problem, or it might not, but since it's free, there's no reason not to. If that doesn't locate the problem, you'll need to find a place with the proprietary Mercedes software to do a scan. The standard diagnostic fee for this should run in the ballpark of ninety bucks, though some might offer it as a free or cheap service to get you in the door. Call around. There are lots of Benzes in Portland and I would expect there to be some competition among them to get new customers.

How expensive is too expensive for you? I always anticipate having to put a few hundred into any used car purchase, and that's with me doing most of the work. If you're paying someone else to wrench for you, that almost always costs more.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.