Supply and demand. A lot of sand, OD, green Scepter fuel cans were made, and continue to be made. Red and yellow, not so much.
Personally, I don't see how placing something in an auction can be called gouging. You don't like the price, you don't bid. As for selling somehting here for a price above what you paid for it, what you feel is an acceptable mark-up, someone else could see as gouging and someone else could see as a bad business decision.
Me, I managed to locate one red MFC and one yellow MFC, both used. The exterior of each was in fair-good shape, but the red one was missing a gasket and the flange was broken (hopefully locating a replacement flange soon). Took lots of patience, and paid a small premium for the cans, though NOTHING, NOTHING, NOTHING like what the new eBay red cans have gone for.
Herb