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
Have you thought about charging $3 / month, or maybe $12 per year for this instead of a one-time purchase?
If you're saving / hosting the layouts, in which users can come back and create new ones or alter old ones, it jives nicely with charging on a recurring basis.
Throw in another service or two on top of what you already do, and the value proposition just keeps going up.
If you've got it working well, there are (smallish) hosting companies that might be interested in white labeling it, assuming it can support templating as well.
Marketing is by far the hardest part!