Over the years we have had a log burner, open fire and LPG, and at the moment storage heaters, which are working out at about £20 a week but we are warm. The deciding factor for me is insulation and I would spend all I could afford on that.
A couple of weeks a go we visited some friend who living off grid, they have a wood burner and a solid fuel aga, literally all the heat goes out the window and the uminsulated walls. We are living in an asbestos shed, made up of two thin sheets of asbestos, but we lined it with insulated plaster board, this has made all the difference, even though its only half an inch thick. So I would spend my time and effort on insulation how ever time consuming and buy in the logs.