The original Avatar had an estimated budget of almost $240 million and $1 billion would see these four sequels average $250 million apiece.
To be clear, $1 billion is almost certainly the low-end estimate for what filming four of these movies will cost.
While there will certainly be some cost savings that comes with making all four movies together, some efforts that would have been done four times over on separate shoots may only need to be done once here, it’s also been nearly a decade since the original Avatar was made and most costs have simply gone up since then.
Zoe Saldana’s salary demands have almost certainly increased in the last few years as she’s a much bigger star now, and we don’t know if she decided to give James Cameron a bulk discount.