Propane is more expensive to be sure , maybe you could go with the method we used years ago . Two stacked 55 gal. drums , the lower one as a fire box and the upper as a heat storage/ exchanger filled with old cast iron cylinder heads . We would get that thing red hot using scrap wood off construction sites , kept us toasty for hours but the EPA would probably have you under the jail these days . There are some waste oil burners that do pretty well for emissions , my brother in Utah has one at his maintanence shop and it works well .