hello there, default price for the game is 5 $(thats the suggested price). The update itself cost 3.75$( now it’s 50% sale because of itch’s august sale). The next update will be 4$, etc.
If you pay the suggested price of 5$, all of the next updates you can download for free, because you payed more then the price of the next update.
The third option is to wait this update become free when the next one is published.
Best wishes
Milo