The combine production budget for Avengers: Infinity War Part 1 and Part 2 is reportedly one billion dollars, according to Bleeding Cool.
The production budget on Avengers: Age of Ultron was about $280M, so it seems reasonable to believe the production budget on Avengers: Infinity War Part 1 and Part 2, being shot back-to-back for nine months in 2016, would be around $600M, maybe $700M. If you had to push it maybe you get to $800M. But, $1B?! That's a lot of clams!
"And of that, the above the line costs, that paid to the screenwriter, director, producers and principal actors will be a cool four hundred million dollars alone," BC reports."And of the actor budget, Robert Downey Jr gets half."
They also claim that Avengers: Infinity War doesn't have a script or a plot at this very moment. If that is true, then any report on the production budget is merely a guesstimate. You can't figure out a production budget without a script. Simple as that.
The films are being directed by Anthony and Joe Russo (Captain America: The Winter Soldier, Civil War) and being written by Christopher Markus and Stephen McFeely.
Avengers: Infinity War Part 1 arrives in theaters May 4, 2018 and Avengers: Infinity War Part 2 will arrive May 3, 2019.