I created a simple SaaS app, https://www.pageblox.com/ that makes $300 dollars a month. I think that in a year or slightly more it could break a thousand a month if I market aggressively. I think I was able to pull it off by targeting a very specific problem and its accompanying keyword phrase: "css layout generator". Over-simplifying, the steps are: 1. find a problem that people and have and its niche, low competition keyword that get about 5000-8000 searches a month 2. build a web based app that solves that problem 3. grow your traffic 4. a/b test and iterate

Marketing is by far the hardest part!