What is the cheapest gun ever made?

Hard to say. The cheapest I have ever seen was a .22 Short "zip" gun, made from a length of automobile radio antenna. During WW II, Phillipine guerillas made shotguns from a length of water or gas pipe, string, and a hand carved bit of wood. In the 1897 Sears catalog, they did advertise a .22 Short revolver for the incredible price of 69¢. Yes, 69 cents