We've built a couple of saas businesses without any investment, as complete unknowns. It's doable, and today it's easier than it has ever been. You can go from 0 to revenue in less than 6 months. The big problem is that there is a ton of software out there, including free software, and people will only pay if your product is much better in some way that actually matters. If you only give yourself a few months to build a product you can only build a couple of features, so those features better be really good.