Follow this comparison and I think you will understand. Corn has about 500,000 btu per bushel and propane has about 100,000 btu per gallon, hence a 5 to 1 ratio. It's highly unlikely that you will find propane at that price anywhere. On the other hand, I have a few customers around the country that are actually paid to haul off the biomass fuel that they bring home to burn. For example, in Arkansas every year there are tons and tons of rice by-products hauled out and burned just to get rid of them.
Similar waste goes on in virtually every state.
Whole cities could be heated with what we are throwing away. You won't believe this, but it just so happens that I carry a full line of furnaces, boilers, and stoves. It occurs in crude oil, in natural gas, and as a by-product of petroleum refining. Propane burns in air. It produces carbon dioxide and water as its final products, and has clean-burning properties.