Oh boy, big question.
To be honest, it is possible to make a film for free. If a filmmaker calls in favors so that cast and crew work pro bono with food and other requisite items donated for the shoot, the cost might be negligible. But… This scenario is really only feasible for small projects like a student film or an ultra low-budget short.
The films backed by a production company or studio with an established cast and crew that get distributed via theaters or streaming or both often come with a hefty price tag. The unfortunate truth is that making movies is expensive… like millions of dollars expensive.
All those superhero movies of the last two decades tend to lead the pack in cost largely because of the A-list Actors, huge sets, and extensive visual effects that are typically part of them. One of the more recent, Spider-Man: Far From Home, came in at a modest $160 million. However, Avengers: Endgame more than doubled that figure with $356 million1.
While those figures represent the very upper echelon of filmmaking budgets, in most cases film production is the most expensive part of making a movie regardless of overall budget.