These and other materials (dice, measuring tools, glue, paints, etc.) all make Warhammer 40,000 expensive as far as gaming hobbies go.
The rulebooks and miniature models required to play Warhammer 40,000 are copyrighted and sold exclusively by Games Workshop and its subsidiaries.
Note: The overview here references the 9th edition of the rules, published July 2020
Games Workshop, Citadel Miniatures, Forge World