Most the stock tank heaters I've seen are at least $35 bucks...cookie tin heater can cost nothing if you have the parts around.Remind me again, why do so many people seem to prefer the lightbulb over the significantly more efficient, less dangerous, aquarium/watering trough/water heater element based designs?
You can buy a good trough heater for $25, and it's going to use less electricity, and it's not going to start a fire.