There are lots of variables based on where you live and your rates but I can say that in NorCal I average about $175-$200 per month for 1000w
Thats a nifty little calculator but fails to take into account peak use fees and base line usage percentages.... Electric bills can be fairly complicated.
I averaged in some fans into my original number. My rates vary but are often in the $.35 - $.45 KW/h .... it depends on how much I'm over the baseline usage.
With a big light like a 1000w comes heavy ventillation, circulation etc. If you have a 400cfm vortex running constantly and a 1000w on 18/6 and say you're growing hydro so you have a couple air pumps or maybe 1 submersible. Things add up, my bill went up a good amount and I have a small setup. Again it does depend on where you live.