I looked but could not find any plugins to do something like this. If there is a plugin please post a comment. This plugin would allow you to create a sign that users would click to buy a command. Commands could could be active for a full minecraft day or be one time use. You could buy commands from a sign more then once and the would stack up. For example if you purchase a command 10 times. You can use it 10 times. This would have to hook into vault for the economy portion of it. The econ program is BOSEcon. A sample Sign [Buy command] 10 /kill 1 day [Buy command] Price command Time till expire This plugin will use BOSEconomy for money.