Greg, for most parts, we like to go through FastLane since they support this web forum. For "OE dealer" parts, like the wood trim, FastLane has to buy it from a dealer themselves, then mark it up & sell to you. At least as far as I know they do!
So the best way (
AFAIK) is to go dealer direct. I know Caliber Motors in SoCal (
www.calibermotors.com) sells at wholesale, and I've heard that Fletcher Jones does as well (another SoCal MB dealer). Also, Rusty (rusty@mbz.org) usually sells at wholesale, via a dealer connection he has in Florida. Note that MB's "list" prices are just a guideline for dealers, and they can charge as much as they want. Some only lack the gun and the mask, if you get my drift. :p It pays to be informed. Here's a link to an older MB USA price list... it's an 8MB Word doc, that shows dealer cost, "wholesale", and finally recommended list prices:
http://www.meimann.com/docs/mercedes/MB_PriceList_Nov-02.doc
Note there is no decimal point so "18900" means $189.00. Also note that this list is 9 months old and MB has jacked up most prices another 5-10% thanks to a weak Euro currency exchange rate. It's still a handy reference though, along with the EPC (Electronic Parts Catalog, the dealer's "electronic microfiche"). The EPC used to be for sale all over eBay but have vanished recently, I wonder if MB cracked down on the sellers? Hmm...
HTH,