I did something similar in the early 2000s. I sold public-domain books (as in created by government agencies) as pdf on cd on eBay. The cost varied between $1-

I did something similar in the early 2000s. I sold public-domain books (as in created by government agencies) as pdf on cd on eBay. The cost varied between $1-$10 with $5 shipping, and would cost me $1.20 out the door. I had everything automated with a robotic disc publisher/printer and stamp printer that I would work maybe one hour a week and bring in a couple hundred dollars each week. It was definitely a great source of side income. The main market was people who didn't search google, since they could take the title of the auction, put it in google, and usually find the PDF right there. There's still people doing the same out there but now the market's flooded and there's much less profit margin available.