Cheap options for boilers

[sploke]

Working on my pot still, I'm looking at different options for the main boiler. I have a 20L stock pot that I use for boiling malt for beer, but its aluminum so I don't think I should use another one for the still. 20L stainless stock pots look to be anywhere from 50-100 bucks online. Pressure cookers are about the same. I'm looking for a cheaper option for something. Its got to be small enough to fit on a regular stove top, and its an electric stove so I think it has to have a flat bottom. Any creative, inexpensive ideas people have come up with?