I agree with what you are saying but some of your comparisons are meaningless. This is my second Mercedes (the first was actually badged as a Mercedes) The parts that are available for Mercedes aren't any better Quality than what I have used on Ford's, Chevy's or the Mini Cooper. The real difference is much lower demand and owners with the means to not care what they pay. Even the BMW guys get much better treatment but there are way more enthusiasts modifying BMW's creating competition.

I looked into the overdrive pulley for Mercedes and see that the crank pulley is also the harmonic balancer which helps explain the cost difference and that you may be getting other pulleys since you only want to speed up the s/c. I would be looking at this a different way. If possible it would be easier to replace only the s/c pulley (and a whole lot cheaper). You can usually put a 15% - 19% underdrive pulley on a s/c engine without having to worry about anything else. I would put a solid mounted pulley on the s/c and get rid of the clutched pulley. Just about no other OEM factory system uses a clutched pulley. Maybe Mercedes did this to get better gas mileage. If you research the manufacturer of the supercharger I bet you will find that there are other pulleys out there maybe used in other cars.