After some debating decided to settle for the following:

There will be 4 grades of completion - v0.3, v0.5, v0.7 and v0.9

- v0.3 - always free, early version as proof of concept. 

- V0.5 - some fixes, could be free. 

- v0.7 and v0.9 - always pay, polished versions with QOL updates and features.