This was New York, but I worked at a movie theater in the Midwest a couple years prior to that and it wasn't that far off. As I recall our matinees were $4.50 and our evening shows were like $7.50 or something (adult tickets). So that's around $25 for a family of four. People would buy multiple large popcorns even though they were refillable just so they didn't have to leave the theater. Back then nearly everyone stopped by the concessions stand on the way in.

Regardless of a $1-2 difference in ticket prices, the concessions prices are pretty accurate from my experience.