Star Citizen became the most expensive game a long time ago. Even when adjusted for inflation, its current 500 million dollars in funding puts it about 170 million above the runner-up, Cyberpunk 2077. Some players backed the Kickstarter campaign ten years ago, and the game is still only in alpha.
So far, over four million players have dipped their toes into the sci-fi world, but not all of them are paid backers. The game often has free trial periods to try and entice more backers.