Ask HN: How to validate a market opportunity in a cost effective way?

tldr; I’m looking for some kind of signal before I spend significant amount of time building something.

I want to build a competing software product for a particular type of small biz. I see in reviews that people are not happy with the leading software provider for that niche. But how should I validate that there is a market opportunity for it and people will actually be interested in it? I tried creating a survey and posting a link on Facebook but nobody took the survey. Survey monkey has a service to get responses(don’t know how they do that) but it’s very costly I.e. $100 for just 100 responses. What are the other cost effective & reliable ways? I’m pretty sure I’m not the first person facing this problem.