Either look at the Kw-hr rate on your bill or go to your electricity companies website and find it and see what your a/c unit will use per hour and do the math. Many people pay different rates so what I could figure for what it would cost me here might be rather different than you would be charged so my figures would be worthless to you.
Regardless, that is gonna be a high bill. Gotta figure that its running 1000 W, 24hr/day.
I would look at a different solution to your problem myself. Aircooled lights, more air circulation, blah blah.