One of the best selling points of a night out at the movies has long been how cheap it was for two hours-plus of entertainment. Not so much when it costs $50 a ticket. That is how much  Regal  Cinemas recently charged for opening night seats in the best theaters to see December’s “Dune: Part Three.” Eye-popping prices for the most in-demand movies on the best screens are becoming increasingly common as the cinema industry copies the audience-segmentation playbooks of airlines and hotels. Theaters are getting people who love movies and have discretionary income to pay substantially more. Some 17% of film tickets sold last year were for premium-format theaters with bigger screens and better sound, compared with 13% in 2021. They cost an average of $18 nationally, according to research firm EntTelligence, and as much as $30 in big cities such as New York and Los Angeles.…