I pay £0.2125 per Kwh. I am running 4 150w TS1000 lights. So at maximum on 12/12 I am burning 7.2Kwh per day in lighting, costing £1.53 per day, or £42 a month, or about $55. Chuck in about 0.5Kwh of fans and you are looking at $60 a month. TBH it is a really cheap hobby, IMHO.