Approximately what percentage of the game is in the demo?
Viewing post in SpunkStock: Music Festival v0.12 Demo comments
The full game will not be completed until later this year. The actual price is not yet determined.
If you played the demo, and enjoyed it, then I'd say yes (When it comes out) ^^.
If it asks for a price when you try to download the demo on itch right now, it is completely optional. You can skip it, and download the demo for free. (it's for optional donation towards development).