What lights do you plan on running?? Im sure if ur looking for every possible way to conserve energy in the rest of the house, your bill shouldn't jump up that much..
Im running a 400W HPS, 175 W MH, some supplemental CFL's, and all my fans and my bill went up maybe $30.
But since I conserve as much power as I can in the rest of my house, it pretty much balances out.