using bukkit 1.1 R3 / precious stone 8 / vault latest / boseconomy 7 :

i'm set the cost of a protection stone to 1000 $, for example when a player having 5000 $ and place one he got a blue message "you do no have sufficient money in your account" but the ps stone is placed and 1000 $ was deduct from his account so that work well, it's just an wrong message. (an you have the same message but in red when you really have no sufficient money)

will be fixed on next version.