I am selling diamonds in the survival world for $55 each, so if you are interested, ask to tp to my chest shop!
My friend has some diamond for sell as well in my town he sells his for $15 each his warp is "/warp JacobLutsy" we are also opening other shops as well but we are still building them at the moment
Honestly that's a little high for the market. They usually go for about $30 on average. You may want to consider bringing your price down some so they'll sell.