Add an auction house just like in FFXI, and remove the AH purchase history for all items.
its worked in World of Warcraft for many many years and it still works perfectly.
Items are sold based upon the time it takes to farm them and supply and demand.
LOOK SE! I JUST SAVED THE ECOMONY!
i'll never understand what they were thinking putting in a history in a virtual economy full of undercutters, what did they think was gonna happen? lol