20-30-% off is relative. Where to get the best price is almost a science. One of my local dealers wanted $115 for a set of OEM Mercedes floormats for my TD, that's with my MBCA 10% discount. Yet a dealer in Maryland (found through "The Star") was selling them for $78. Even with shipping it was still cheaper to get them through them. They mentioned to me that the "list" price was $106, so obviously this local dealer was making a killing profit on their prices. I suppose it didn't help that it was Princeton ($$$)Mercedes.
BTW this same Maryland dealer was able to get floormats for my neighbor's 1980 300SD, for the same price. This is a chassis MB stopped making in 1980. I called a local Ford dealer to see if floormats were still available for a '93 Taurus (used to own one), they said no, only 1996 and newer and they were $70. Chalk one more up for Mercedes-Benz product support.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member