I would think the price of a set of chips would be stable after about 6 months.
Chips just released are often higher due to the interest at the time, collectors and dealers hoarding the chips and the hype!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
The person getting $280 per set is probably the same one that can't get $125 later and still has (197) sets left to sell after they've sold three.
Sometimes these hoarders even end up returning many of the chips they originally bought from the casino in the first place.