The cheapest stoves I've ever run across are made of cast iron, such as the small pot belly stove or the boxwood stove...both can be had for less than $100 as many building centers.
In my opinion, the biggest drawback of cast iron is that it can crack and leak. All joints on cast iron stoves are bolted together with a gasket between the sections. A crack in a cast iron stove is very difficult to weld. The cast iron cracks when heated too fast.
My recommendation has always been to buy a good quality, American-made, plate steel stove (1/4" to 5/16" steel).