I created my first Ruby on Rails SAAS few years ago. My goal was to earn $5 and call it done. But within 2 hours I made $12 and I was ecstatic. That year I made $2000 from the site. My overall expense was just hosting on Linode and time I took to learn Rails and develop it. I no longer run the business actively as it was very hard to reach the ideal market.

its still there! http://www.residencymail.com