why movies cost high

It really depends on the film.
For major films one of the highest costs is often the salaries for all the above the line people— actors, directors, and producers. But, as that increases costs there, so to do the agreements with the unions of the below the line workers (from the DoP all the way down to the PAs, who don’t have a union though should) as their rates are often tied to the overall budget of the production.
From there your costs come down to locations and permitting, the costs to build a set, the costs of wardrobe, the cost of background, the cost of FXs and and so on and so forth. Also there is the cost of all the equipment needed to make the movie— perfect example, the Arri SkyPanel. I know most don’t know what that is, but it’s a light used on mostly EVERY set now that it has come out. The rental cost for one is $200 per day (S60, in LA). Sure you’ll get a discount for a long rental; but when you consider you might be using 100+ Skypanels for a SINGLE set for a SINGLE scene, in addition to all the other lights you might need (and the crew to hang them all and the DMX unicverse to control them all)— well you see costs start to add up quickly.
Hell on a feature film you may spend $200 easily on clothespins! or $500 on Tape!
And thats not even getting into all the other office-style costs of a movie (paper, office space, production accounting, internet, etc etc. )
Basically EVERY film is a whole start-up company on top of being a movie as no studio “makes” a film— they all form LLCs to make the film to limit their liability (like StarWars Movie 999920222 LLC, not a real company).

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