The easy way to figure this is to see how much one kilowatt hour is and then decide how long it takes for the lights to use 1KW. CFLs and fluorescents don't use a whole lot of energy, so it shouldn't make much of a difference if you're only running 5. Say you use 200W total, it would take 5 hours to use 1KW. If you run your lights 24 hours a day, you're using about 5KW per day. Take that times your KWH cost and viola; your daily cost.