You can buy the Beta version of Due Process now for $24.99 or your regional equivalent. Buying the Beta will also grant you the Early Access version and the full release version when they get released.
Please note, that the Beta is sold on an unlisted store page. You can only purchase the game if you follow the link above. Additionally the Beta is limited in access - meaning that the store page might go offline for long stretches.
More details:
https://dueprocess.info/blog/2020/8/19/limited-access-beta-has-started