If you have a crawl space or basement, you can install electrical under-floor heating at fairly affordable costs. Basically the heating element comes in a roll which you then tack the the underside of your floor.

I have lived with such a system before for a year and it was both easy to use and did a good job of heating the space. I don't remember the electricity costs so I can't comment on the economic efficiency, but AFAIK it's moderately good. I wish I had it in this house instead of the noisy, draughty, and inefficient gas-powered duct heating which I avoid switching on whenever possible.