Movie stars get paid orders of magnitude more than top martial artists/musicians/dancers, so more people try to be actors, so there's a larger market, meaning instructors can charge more.
Also depends where you're looking. The professional acting scenes in LA/NYC tend to choke out the hobbyist scenes (why see a community theater show in Manhattan when you can get sub-$50 tickets to a Broadway show from TDF?), so if you're looking for acting classes in those areas, they're directed at and priced for professionals.
Movie stars get paid orders of magnitude more than top martial artists/musicians/dancers, so more people try to be actors, so there's a larger market, meaning instructors can charge more.
Also depends where you're looking. The professional acting scenes in LA/NYC tend to choke out the hobbyist scenes (why see a community theater show in Manhattan when you can get sub-$50 tickets to a Broadway show from TDF?), so if you're looking for acting classes in those areas, they're directed at and priced for professionals.