There is no indication that Marvel will confirm the production budget for Avengers: Infinity War, with just one week left until the first sneak peek screenings are held on Thursday, April 26. Filming started on Avengers: Infinity War in January 2017, wrapping in mid-July 2017, with filming starting on Avengers 4 in August 2017, wrapping in mid-January 2018, completing roughly an entire year of production for both movies. That was also during a time when Marvel was planning on shooting both movies simultaneously, although they ended up scrapping those plans.
There was a report from a few years back that claimed the combined production budget of both Avengers: Infinity War and Avengers 4 would be $1 billion, meaning that each movie would cost $500 million apiece. Many times, official budget numbers are never made public, but it wouldn't surprise many if Avengers: Infinity War did cost upwards of $300 million, or even $400 million. While neither budget has been confirmed, a new report claims that Avengers: Infinity War had a production budget of nearly $300 million, although an exact figure was not divulged. While the original report was never confirmed, it claimed that both Avengers: Infinity War and Solo: A Star Wars Story had production budgets of roughly $400 million, which would be enough to best the all-time record of $378 million that Disney spent to make 2011's Pirates of the Caribbean: On Stranger Tides.
Earlier this week, a report claimed that both Infinity War and Solo: A Star Wars Story may ultimately tie for the distinction of being the most expensive movie ever made, but now another report claims Infinity War didn't cost quite so much.