Ouch. One thing I have learned in my time as a service writer for those things: Mercedes are EXPENSIVE to work on and yes they have mediocre at best build quality. All that leather and fancy wood don't mean squat. Well, it is nice to sit in while you wait for the tow truck.
That car has a habit of breaking two plastic levers in the HVAC system, this shows as a clicking noise and non responsive footwell vents (real bad problem in winter). $15 part, dash has to come out, $1200.00 total. They do that a LOT. 02-04 was worst but I have seen 06's do it too.
The rear SAM module runs all the lights in the rear. You think you have a bad bulb, nope it's the SAM. Can't go without it, you'll get tickets. Plunk down $500.00, please.
CD changers die a lot. Remans are finally available, $450-$500.
Some of the V6's of that era have a problem with premature wear of an idler gear in the timing chain setup (this was more a E class problem but C's use the same setup and some ngines fall under the same bulletin). 22 hours labor to replace. No that is NOT a fatfinger, 22 hours. Plus parts etc. Call it $3500.00. This shows as a Check Engine light and a code for a camshaft position solenoid failure, because it's clogged with metal fuzz. Mercedes does NOT cover this past the 80,000 mile powertrain warranty, good luck if you are a 2nd owner trying to get a goodwill adjustment.
Differentials have a nasty habit of leaking at the axle seals. The diff has to come out. $900.00, please. Did you run it till it dropped? A salvage yard unit will generally set you back $1200 or so.
Ball joints are made of pot metal. I see 60K cars with intact boots with sloppy ball joints. If they get unlucky and have to replace both the knuckle joints and the ones that are made into those stupid thrust arms, pony up $1100.00.
The CAN systems are (as Bishop the android said in ALIENS) twitchy. There's no easy 'reset' if it goes stupid, don't believe all that 'just disconnect the battery' hooey. That may or may not work. If it doesn't (very likely) you have to plug in a computer and teach the car everything all over again. That's a minimum of $125.00 anywhere. If there's a module bad bringing the 'bus' down, bend over and grab your wallet cuz here it comes. Quite common: seats that go forward when you want it to go back and it won't respond to any inputs to make it go back. That's a seat module, congrats you just spent $600.00. If the switch caused the module to ralph, add another $500.00.
I get those $149 brake jobs in all the time with them screeching. Mercedes says don't resurface their rotors (not enough extra material) and the cheapo pads sound like fingernails on a chalkboard. Average cost for GOOD pads and rotors PER AXLE is $575.00, a bit more if it's a Sport with the cross drilled rotors. So 4 wheel brakes that don't screech = $1200.00.
For Gawd's sake, talk them into a Honda or similar. Sure there's no 3 pointed star to show off to the neighbors but they'll spend more time driving and less time cussing an expensive broken car.
