Then wait for the game to be finished, and pay money for it then. Treat it like a normal retail game which you get when the developer finishes work on it.
Since there are [nearly] no publishers to back adult game developers, they can't develop games in private like a normal studio, so you get to see semi-public funding and access models like patreon.
However expecting to have your cake (not paying towards development of the game) and eat it to (get immediate builds of in-progress development), like it's something you deserve, is just freakin' greedy. Whether you are poor 3rd world student with bed-ridden mother, or a millionaire in Hollywood. Stahp.