A bit cheap maybe, but it really depends on the situation. Usually in the beginning gems aren't worth much but later on the going price does increase considerably.
If you're planning on stocking on each gem in order to facilitate a working DICE, good luck. But wouldn't it be easier for two parties just to agree on exchange with a middle price, thus saving money and cutting you off?
I personally felt the market thread of Perpetuality worked quite well with exchange economy. Yet if people insist on bringing capitalist market devices in essentially non-capitalist environment, feel free to prove me wrong.
