How much electricity($) does my logitech z2300 use if left on continuously?

I. Have this system but no remote comes with it so I ve been wanting to just leave it on constanly because it's connected to my iPad which I am always on and at random times i watch videos, YouTube, pandora etc but not often for sound apps. but it's become a real pain having to go back and forth to the speaker to turn the power on, this is the reason I bought a bluetooth receiver for my speakers so I wouldn't be confined to having to be close to my home theater to use it. So I was wondering how much electricity in terms of $ would I use if I left these speakers on without ever turning them off over the period of a month. Keep in mind that I Use it randomly not often so they wouldn't be constantly playing but just on. It's a pretty big 8 inch sub with 2 speakers and a wired remote.