Check around for used copper hot water baseboards as well. A regular domestic hot water heater can heat a fair sized run. A system with used everything can be built pretty cheap. A system with free everything can be a whole lot cheaper. A recycled hot air furnace will heat a shop pretty well and the blower only can be used as a fan in the summer. Heck, you could add a/c as well. Look for a house that is about to get torn down and see if you can salvage the heating system, scrap what you dont need.