It is maybe not the money. Where I live, 100 bucks don't merit the bureaucratic effort of income anyway.
I personally am hesitant to work with code others have done and say "it is buggy and I don't know why". Don't get me wrong, I do a whole lot of buggy code myself, I am not a professional ;-)
And I second @duane, also because of the requirement "beta 2+" that is too relaxed a definition IMHO. The risk of having to visit the same code multiple times and probably introducing new mistakes in the act is high. There are still warnings out of potentially breaking changes to Godot until release.
I would wait until Godot has been released for production use (I actually do so with my project that involves a lot of C++ boilerplate code). After release, I suggest you work through the documentation and determine if your project as a whole fits into 4.0 with only minor changes, or if it needs a complete overhaul because basic invariants it relies on have changed.
Just my 2 cents ...