shutdown on inactivity

I have two ReadyNAS Ultra that i use for movies storage.

I have configured XBMC to automatically wake-on-lan the NAS when it starts.

Problem is that i now need to find a way to automatically shutdown the NAS after a period of inactivity (say 2 hours) because i dont want to let the servers run 24/7 and it is annoying to have to physically shut them down all the time.

Someone told me a couple of months ago that it was possible to write a script to do it. But i don't have the necessary knowledge to do it myself. If someone can do it, i can pay money for it (through paypal).

Any help ?

thanks