I agree with everyone. My tanks got blamed for the jump in the electricity bill, so I paid up. BUT, when my grandmother moved out, the bill dropped by half! Ha, the tanks are still running and the bill has stayed low. We get free water where I live thankfully.
Electrical consumption can vary widely. You could have an unheated tank with a 20W light over it and 20W for the filter. This basically will not even change your bill over its standard deviation. But if your setting up something larger, like say a 240G with a couple big return pumps, 500W or more of lighting, over 1,000W of heat to keep it about 10-12*F over ambient (80* in a 66-68* room), then it might impact the bill a bit. I close to doubled my bill from being super conservative to now having 2 computers running 24/7 and 4 tanks (largest being 75g). Will be putting in a 240 and 150 soon though. Water bill will probably go up by as much or more so than electric I beleive. Water (and sewage) isnt cheap here. FWIW I think electric hot water heaters are one of the biggest consumers of electricity in your house, my folks just replaced their electric one for a fuel oil one and their e-bill was cut in half.