im trying to set a price for each stone, and i set the flag but when i use the block nothing happens, place the block is already free :S
I tested using iConomy and using BOSEconomy and nothing happens, the blocks are still free

Can you post or link a copy of your config.yml?

Yep. Once I place the price flag on a field, only ops can place the field down, everyone else will just place a normal block.

Giving the preciousstones.bypass.purchase to them though will allow them to place the field but then it defeats the purpose of the price flag.

Here is my config : http://pastebin.com/wrn4SP5G