a 100 watt light in a reflector socket is about as cheap as you can get. socket $9.99 and bulb 2.00. focus bulb on the side of the watering device and plug it in.
Best way to keep water from freezing? - Page 8
I used an aquarium heater last year and it worked perfectly, but this year I somehow fried the aquarium heater and it broke apart, leaving black sand and murky water. I think it is a good way to go, but I would just recommend you check inside the bucket frequently to make sure everything is working okay.
Edited by chococharly - 12/16/15 at 9:36am