At $0.15/kWh (you're probably over 'baseline' useage), thats about $35/month.
Now you could get creative, and say, run the tank lights inverse of daylight, if you have Time Of Day metering (its cheaper 7pm-7am more or less)... But that just silly
55g reef, 2x250W 10k MH
+ 2x96W PC
actninc, 10g sump, AquaC Urchin skimmer, 65lbs LR
xenia, mushrooms, wels. open brain, fungia radiata (orange), green eyed zoos
flame angel, mated pair of false perc, 6-line, firefish
20gH electric yellow cichlid