as far as the best thing for a cfer it would be an electric, the best on your pocket can differ from where you live, i'm guessing that you aren't in the US just because i have no idea where you would get coal around here, i guess universally a wood burning heat source would be cheapest cause you can burn just about anything in there, if you're looking for clean burning propane or nat. gas because there is little to no emissions. dang i sound like hank hill with the propane but it is indeed the best as far as gas fuels go