CFL's will keep your bills right down and will deal with any heat issues you might course by switching to 24/0. They are also cheep to buy and easy to get your hands on. What lights are you using and how's the ventilation on your grow room?
I have conducted an experiment with cfl lights to create the cheapest energy to bud. I have managed to veg a single plant with a single 26 watt cfl bulb. For the flowering stage I had to add an extra 26 watt cfl bulb. This dose work but was not to effective. I have also used 3 26 watt cfl bulbs...