During the 1930s through 1970s, a popular "work at home" scheme was writing and publishing your own pamphlets and booklets. Advertising was through the classifieds in popular magazines.
Priced at $5 or less, you could find home-brew booklets on just about anything. The consistent sellers were those that provided information not generally found at the bookstore or library. Copies were mimeographed, and for the bigger outfits offset printed.
Checks Stuffed Into My Post Office Box
I'd always wanted to try this concept, but I came to it a bit late. By the 1980s the market was starting to dry up for mail order pamphlets and booklets, but specialty books were still fair game.
In 1986 I wrote a 100 page book on building your own PC - one of the first of its kind. I spent about $30 in classified ads, and mentioned it in a magazine article I wrote.
Within days of the ads and article, I started getting orders to my post office box. I priced the book at $12.95, including shipping. It was printed on my own office copier, and plastic comb bound. Over the next several years I sold some 2,600 copies through the mail and at local computer swap meets. One swap meet alone I sold my entire "run" of 100 copies in a single afternoon.