We have an outside furnace and love it. You will save money if you have your own source of wood. It is work to get enough cut an stacked for winter but well worth it. Since our furnace heats our hot water we save money on our electric bill also. 

I live in Pennsylvania and we have a festival called Ag Progress days. It has all kinds of vendors demonstrating different things. Ours was $3000 but that was 6 years ago. If you buy one make sure you can get parts (for the blower, circulating pump etc.) quickly. because the laws of nature are it will break when the temp. is below freezing. Some of them do not heat your hot water but that feature is wonderful. Ours is a Hardy Outside Furnace. We love it. As far as the investment furnaces are not cheap and fuel oil is more expensive everyday. Besides this furnace is outside less risk of a house fire. If you have more questions I will try to help.

Theresa