~100$ / year from an Amazon Price Tracker (http://www.rankique.com/ http://www.rankique.com/) I wrote a long while ago. It's 100% passive and is free to run, a

~100$ / year from an Amazon Price Tracker (http://www.rankique.com/ http://www.rankique.com/) I wrote a long while ago. It's 100% passive and is free to run, although some SEO should increase that, which frankly I neither have the time nor the expertise to do.