I have found that just placing a regular electric heating pad in my fermentation chamber will provide enough heat to keep the temperature from dropping too much in the winter. My chamber has a digital Johnson controller to apply the cooling. That controller is left at the desired fermentation temp and the heating pad is mostly uncontrolled. I say mostly uncontrolled because most pads have a 3-position power switch that allows me to dial up the energy input when needed, or reduce it if the cooling system is coming on too often. Its the way to go and its cheap. You can find heating pads for around $15. You do need to find a pad that does not have an automatic shutoff timer in it. They are available.
Oh, and you can use your heating pad for your aches and pains too.