Bikes designed for heavy touring tend to be rather expensive. No bargains to be found. However, I have noticed that some "entry level" mountain bikes have the longer chainstay length, wheelbase, and headtube angle needed for a "loaded" touring bike. If someone was going to "modify" a non-touring bike for touring, a less expensive mountain bike might be the way to go.
I have seen Trek mountain bikes from the 1990's (top grade steel frames and steel forks) selling on E-Bay for around $100 or so. With light weight "slick" tires, such bikes could be modified into useful touring bikes.