Cost: $50 and up for a homemade unit.
One of today's ultimate workshop conveniences in the wintertime is to have a heated garage. Attaining this with either a gas or electric heater is both expensive and carbon costly. However, if you can harness the heat from the sun, you can have your heat and not feel guilty about it. The labor involved in building such a unit is fairly straight forward as long as you have a few basic hand tools and craft experience.