There's a huge difference between HTTYD 3 and the latter two. Just in terms of the environments, water effects, and lighting, Frozen 2 and Toy Story 4 blew away any other animated movie released last year. TS4 cost more because Pixar actually develops their own technology for their animation (part of the reason why so many people, me included, would love to work for Pixar's tech division) while WDAS just uses Pixar's tech.