$1 wood pellet burner for outside heat
Keeps outside animals warm and can be used as emergency stove, a handful of pellets burn for 45 minutes +, a 40 lbs bag of pellets costs under $6
Make a few holes with a screwdriver and hammer at the bottom of the $1 clip holder (from the dollar store)
Also, adding a usb powered fan that you can purchase for two dollars to the previously suggested tealight candle heater will circulate the heat more efficiently
We’re working on a write up close to this post.
Take a metal coffee can (or similar) and arrange it so it’s above the candles. The sand makes a thermal battery. It will heat up and release its heat slowly.
You can do similar with larger metal containers and sand by placing them on a wood stove.