• Seal up any cracks in doors and windows. Your door might need a special tool for realigning before sealing. A professional can do it well for $200.
• Insulate any wall that feels cold to touch. Old mattresses, rugs, book shelves, wooden boards...
• Cover your fridge and freezer with styrofoam...
After having plugged all the small air leaks in my windows, I'm thinking about stopping the cold wind from the outside by building a tent outside of my door and windows. The wall gets cooled down faster when wind blows directly against it, so just stopping the wind could potentially save 50...