400 watts is nothing. When people get caught because of energy usage it's usually for like 20 1000-watt lights in the basement or something.

Your setup probably draws closer to 500 watts with the ballast, so assume 1 kilowatt hour will run your setup for 2 hours. A kilowatt hour of electricity usually costs 10 cents or less. If you're running 12/12, that's 60 cents a day.

A bathroom vent fan would work well, if the noise doesn't matter and if you have somewhere to vent to.