"So we're trying to figure out a way working with [director] Juan Carlos [Fresnadillo] to get the budget down and still keep so it's true to the core audience."
Hey, good news: I have a perfect way to solve both problems at once: DON'T MAKE THE MOVIE. As much as I loved this game's basic story and as much as I would love to see it turned into a film in order to reach a wider audience, it is fundamentally incompatible with a film. The whole twist of the game hinged on it being a game, of revealing to the player, a fully conscious, fully willpowered individual, that he's being duped and has been blindly following instructions the whole time. That does not work in a movie.
Furthermore, the twist hinged on a gambit so elaborate as to border on ludicrous: genetically engineering a person who has half of Andrew Ryan's DNA, ages super-fast, and responds to mind-control; sending him to the surface only to immediately afterward return to the city as an "outsider", will all memory of the above conveniently replaced with a fake history. It worked in the game because, again, it's a game, and the player is experiencing it all from a first-person perspective, with only minimal backstory to go from at the beginning. Put it in any other medium and people will never buy it. Even M. Night Shamalyan would laugh at a twist like that.
They would have to completely change how the story ends. Who the main character is, what he's doing there, how everything gets resolved. The backstory of Rapture is plenty to build from, of course, and it's not like a movie hasn't been made that ignored the plot of the game entirely (much rarer is a movie that didn't... I can't even think of one offhand). But the "core audience", the people who played the game, will complain that "They changed it, so it sucks."
