You could use a kerosene heater. Home Depot has one for $129. It puts out 23,000 BTU which will keep you toasty on the coldest nights.

I am not a fan of these. They need to a source of ventalation. I suggest cracking up the window when you use it.

Here is a link that might be useful: Home Depot Kersosene Heater

Any fuel burning non-vented heater will add lots of water vapor to a room. And a potential for carbon monoxide. I had a case where a church wanted to heat a room of about 400 square feet on an irregular schedule but the heating set up required heating 8000 square feet, all or nothing. The 8000 feet was on a setback of 50 deg. So I installed baseboard electric in the room with a low voltage wall thermostat (under a security cover) in series with a spring wound timer and a silent relay controlled by the timer/thermostat combo. Turn the timer and get heat for a maximum of 12 hours. Reset the timer if occupied for longer times. No one could tamper with the temperature setting and no one could forget to turn off the heat. With unpredictable and irregular use, a programmed thermostat was not appropriate. The baseboard had to raise the temperature from 50 (the setback) to 70.

fujitsu heat pump

The ratings for the linked Infrared heaters are 500/1000/1500 Watts. How's that going to "cut your electricity bill?"