Heat a whole room for under 15 cents or possibly even cheaper if you find cheaper candles or maybe larger ones.
What you need:
Small candles such as the ones seen is the video which are found at Ikea
A metal cake pan
Two clay planter pots, one smaller than the other
A lighter to light the candles
This awesome idea works on convection, which is accomplished by the air moving around between the two clay pots. This helps create a forced air effect which pushes the hot air around the room.
Video: