If you purchase on itch (32$?) you will get all updates, just update your version via the Arrow Down icon top right next to your name and click "My Downloads" whenever there is a new update.
On Patreon i believe you pay less (was it 10-12$?), but you need to pay again for each update (since you need to become a member each time to download it every 2 months if you unsubscribe each time).
On Patreon there is a monthly cost.