Yeah from what I've seen the best ballasts give off alot of heat. But you can pick up ballasts that are warm to the touch after a hole days use. Try www.growell.co.uk, you said cheap, so there you go. All of thiers are switchable as long as the wattage of the light is the same. You have the bulbs free but generally if you didn't and you wanted to save even more money, you can get duel spectrum so the bulb is the same throughout the entire grow. I've always thought that it puts too much stress on a bulb having it on for such a longperiod of time, when you could just switch bulbs. Alot of people get duel specs though. Growell also sell ballasts with contactor and timer built in if you want to spend £££££.