That really depend on the tank setup. If you run multiple filters (I do) and use plants (4x40W NO fluorescents on my 55), I promise you it will be higher than $1.00 per month.
4x40W x 12 hours x 30 days= 57600 watt hours, or 57.6 kilowatt hours. I pay $0.065 per KWH, so 57.6 x 0.065 = $3.74 per month for the lights alone, ignoring the ballast factor (my units are old, so an additional 15-20%) and the filters, and the heater if you need such. But you can calculate based on the power usage of your own equipment.