I have fallen for the model of "If I can get this percent of this market segment I'll be able to gross this amount monthly". I realize it's not an accurate method and am looking for recommendations on ways a cash-poor self-funded startup could analyze the market and get real feedback from actual potential customers -- both to accurately determine the viability of the product and to assist in acquiring seed capital to take the product to market.
Looks like you have a problem.
Based on what you've provided, you made the SaaS before confirming there were buyers for it.
Biggest mistake I see in SaaS. Second is trying to sell by Demo (features presentation) and believing that's going to work.
Better find some buyers.
I'm not seeing a demographic. Industry, size of company, department the SaaS best helps, who the stakeholders are that are involved in the buying decision, budget, problem(s) solved by the SaaS and so on.
Those are the things you'll be able to use to estimate the market size.
Right now you need customers. What pain points do they admit to having that your SaaS fixes?
When you get some customers, what are the commonalities? Do you have some already that you can look at?
Then you can tune your marketing to point at the type of companies, people and problems buyers admit to having.
That's the key, though: they must admit to having the problem.
If you don't have that, if you don't know why people would buy your SaaS, you're in real trouble. And I'm not talking about what YOU think. I don't know how many times I've gotten involved with a market, or started in on behalf of a client, and discovered the issues I thought would be important meant little to real buyers...and the things they valued were a stark surprise to me.
If you want help with this process, you know where to find me ;-)