I usually buy them in stacks of 10 for 200K. Having an active miner, I know what the drop rate is (terrible), and 200K is worth it to me.
If you really want to sell them, drop to 15K apiece - i.e., 150K for 10, and drop em on a Luna vendor

I happen to have an empty vendor space free-of-charge for you to sell ingots and/or gems...
Another option is to sell them at PRAH auction - use a low end price that you can live with and then let the biiders decide the gems' worth.