Or, make them level independent.
err no lvl 50 equipment should not cost the same as lvl 100 equipment to plus it. I think they should implement a trade window where other ppl can put plussing jewel in against an equipment for x amount. the gold goes to the person giving the jewels, and the jewels gets used up one after the other to plus the equipment.
and at the same time, they could implement an exchange of all jewels from lvl 55 to current to be exchanged for the best jewels atm. keep in mind that the price of jewels were fixed for the best jewels at that lvl (I think....)