I agree on the thermostat idea... grab a piece of flexwatt and a thermostat and your problems will be solved. Flexwatt has a greater output than most of the in-store brands... plus, when plugged into a thermostat, you can set it at your preferred temp and it will stay there.

And yes, they can be expensive... however, if you do a little looking around, you can usually find some slightly used ones for a good price. I just purchased three more Johnson's thermostats for only $155... that's only about $51 a piece, which is a steal, really. You can't beat 'em.