Well it all depends on what your states kilowatt/hour price is. At 9 cents a kilowatt hour for a 400 hps I believe it is around $1.08/24 hours. Here is a link to a page that has the kilowatt costs. http://michaelbluejay.com/electricity/cost.html
Thanks, it is actually cheaper than I thought. I usually run about 500 watts for a month during veg which is around $32. Then I go 12/12 for about three months or whatever the breed needs so 32x3=96.. So for me it is around $100 for a full grow(2-3 plants). NICE!
I'm running a 400w hps (digital ballast) on a 12/12 and 400w cfls 24hr and 6 computer style fans 3 110v and 3 24vdc and my bill went up 20 kwh a month so my wife says. I don't know, doesn't seem like very much to me but I don't pay the bill she does.