The vast majority of people don't pay anything for Vaadin as it's Apache 2 licensed. Out of curiosity: Why do you feel you have to spend on it – is it some part of the tooling or are the support alternatives the reason? (I work for the company behind Vaadin, thus honestly curious).
AFAIR, it was the "Grid Pro" and "Dashboard" features that were needed, but they were out of budget for our infant phase of the product and we went with React. It was a long time ago anyway, I last worked with Vaadin 7. I will however say, that I really enjoyed working with it at that time.
