Get a 4 or a 8 outlet air pump from the hydro shop. GH and Eco's are good. They use very little electicity and each single outlet puts out more air than a wally dual outlet air pump.
It also matters what kind of system you plan on. Like the styles that require water pumps. But they are run on timers and the electic cost is insignificant.

My bill was slightly higher when I switched to hydro..but I added more lamps so I cant really give the numbers.