I use oil-filled radiator heaters. I've never had one get too hot, but they don't last nearly as long as an electric heater. I usually get two full winters out of a oil-filled. I always go to Target around this time of year and snatch up the clearance ones.. They sell them for around $20 this time of year, just gotta get there at the right time...
In my snake rooms, I use a thermostat on them, they work great that way. I use them with their built in thermo in my two rodent rooms. Of course, a steady temperature isn't all that crucial for the rodents....