On the site, I see a Steam link on the bottom of the page. And on the Steam page it says "download demo". Maybe this is just a way to get feedback + build a community before rolling out a paid version?
Even if that is just in the sense of "right, current version is the demo from now on, and all future versions are the paid version"
I suggest you gate some key upcoming features and hold on to those until you have a few to "launch" into paid mode.
I'd happily chuck $10 at something like this.
Just be transparent about where you are and what your plans are.
That said, it may be hard to switch now without garnering those negative reviews you are talking about.