If you're already helping people solve a problem online - it may be the perfect way for you to fund and validate your SaaS Product.
For example - if you want to build a cold email SaaS, you could first offer a cold email course that shows people how to make thousands of dollars using using targeted outbound cold emails.
Or if you want to build a LinkedIn SaaS, you could first create a LinkedIn mastermind that shows people how to book meetings on LinkedIn without running paid ads.
As long as the community you are creating is closely related to the SaaS you want to built, you will not only be funding development, but also validating your idea.
When your SaaS is built, you can then launch it to that community, and then pivot to focusing on the SaaS full-time.