This is a simple plugin I made that allows users to get currency every time they kill someone. All config options are in the plugin and it is super light only being about 6kb.
This overrides the default /shop command in order to show the player a different kind of shop where they can redeem their currencies. The command that the item runs is /shopgui, so make sure you are using ShopGUI for your shop plugin.
If you want to add currency to a player, just use /addtokens!