Well if you are growing inside anyway the cost is less.....you will be paying for temp control, lighting yadda yadda anyway. That's the expensive part and it depends on how crazy you want to get with enviromental control so you are mostly talking electricity costs.

I don't know the layout of your basement...do you have access to water easily because you do NOT want to be hauling water for hydro up and down the stairs....you'll go nuts. And do you have a spot to dump your used water down there as well?