For “an entire large game”, like an FPS game, I would expect AT LEAST 200,000 Robux. It would probably take me around a month to program the game to completion. I’d say $700 for a month’s work is alright.
Although, your obby being 5,000 - 15,000 is completely fair as long as it’s mostly just a regular obby, but only because I could finish it in a few hours