I went to the theatre in London pre covid and paid around £80 for medium price seats at a very minimalist production (a cast of about 4 and very little scenery)
You do realise that even a tiny show involves:
Wardrobe mistress who maintains and prepares all the costumes every single day (may also have a deputy and assistant on a big show)
Dresser(s)
Stage crew (minimum of two/three depending on size of theatre, maybe more, at least one of them prob a first aider) - needed not just for the show but also to maintain the building and for safety
LX department - one electrician in the crew room to deal with emergencies (this person prob also a first aider), one on the board, maybe more doing onstage cues or follow spot - as before maintaining building as well as doing the show
Sound department
Orchestra if a musical -could be as little as five or as many as twenty people who are all highly skilled
Stage management (company stage manager, stage manager, deputy stage manager and assistant stage manager - who all have different jobs that can't be combined and aren't all doing the same thing)
Casual show staff for specific tasks/cues
Production staff - electricians, sound and stage people who are tasked with putting the show in and moving it venue to venue (this is a specific job and can't be done by the resident theatre staff)
Lots of front of house staff
Renting the theatre
And so much more...