Cool concept, but could be very hard to do in a market where literally everyone has the potential to be a consumer and/or vendor (so more "rogue" merchants). If you're looking at a forming a generic average, what's worked best for me is to follow the established merchants advertising on the forums (versus the average player trying to get rid of excess things).

Merchants on the forums are in it for the long haul and are consistent traders of items so they represent a high volume of traded goods. And from what I've seen, because they post their prices for all to see, their prices heavily influence online trades.

My suggestion is to find the active merchants on CM and get them to buy into a trade alliance or something to not necessary price fix but rather collaborate on general accepted price ranges. Then it's an activity shared across different folks to maintain too. That might get you closer to what you're trying to do.

But that suggestion aside, I'm with GrinningBobcat to just let it be and let everyone figure prices out in their own way (trial and error & supply and demand). Its easier and requires little work.