Since I started 6 boxing again on 6 computers, my electric bill went up by $80 to $100 per month, but thats also because now I have to keep my air-conditioning on all the time when I play, because 6 computers generates a good deal of heat. Also, this is based on the last month or two and those were the hot months for where I live. I could go down to fewer computers and do two accounts per box, but I like not having to jump between windows. And my main monitor is a 42" 1080p, so probably not very power friendly compared to something smaller.