The problem is following. Once a gem is not supported, the price for it raises up to a silly high, because you have no comparision to an existing listed pink. Then people start farming it and the dumping starts.

The fact is there is no firm price for pink gems, they varies from 10k to 30k to talk about the real deal.

Second tipp is to farm high level gems not weapons. They sell much better and faster then weapons and you can hit higher prices for them in auction.