Powerheads or pumps running all the time can add up. Assume each takes 10W, which is reasonable, and you have 5 of them running 24x7. That means you spend 33.6 KWh per month on powerheads. If you have 400W lighting running 8hr/day, you spend about 96 KWh per month on lighting. Half that if you only have 200W lighting (48 KWh/month). If you have external filtration that will add some costs, too, depending on the type. Heating should be fairly negligible since the heater is on sporadically.
So, depending on your setup, you may very well be spending more on pumps/powerheads than lighting. They're probably pretty close in most cases.
I spend most on lighting, since I have a 400W that runs about 8hr/day.