Sashimi/sushi slot nicely into $$$+ pricing range because the small portions and emphasis on presentation are very similar to the aesthetic often found in high end gourmet restaurants, which tend to serve things that are beautiful, tasty, and tiny.
At least where I'm from there's bimodalism in Japanese cuisine if you count sushi rolls, which can be had dirt cheap (pretty localised/internationalised though). I like cheap sushi here because the cheap sushi game is usually locked down by koreans, so the rolls end up being this blend of kimbap and sushi rolls.
Dunno about Korean restaurants in the west though, have only been to Korean restaurants in Korea.
edit: Wish I was from/lived some place with nice cheap Italian sandwich shops etc, that must be amazing.
To edit further, I think western consumers' perception of a country (as well as what you said about the country's population) affects price as well