Ok, let’s start with some words of caution… Carbon monoxide kills, you can’t smell it and you can’t taste it. The project requires competent welding/join sealing etc. This isn’t a project for cutting corners or shoddy workmanship, as that could get you killed.
That said – if you do have the appropriate skills, you can make an awesome pot belly stove for around $50, which is probably at least five times cheaper than buying one ready-made.
(Photo from: Dr Qui via Instructables)