A knife designed for heavy duty might add to the cost, sure.
To me though, there are plenty other reasons to go with a more costly product.
Heavy duty alone is not always a positive feature in a knife, for delicate work many a tank-like indestructable is borderline useless due to being too bulky and ground for austerity rather than fine cutting.
Refinement, blade profile and grind, filework, scale-materials, innovation and general cost of a modern shop are some of the factors driving the prices upwards on many higher-end knives.
And of course there is the marketing, hype and all that.
A quote from a 1895 barbers manual:
"Cheap Tools Is Misplaced Economy. Always buy the best and highest grade of razors, hones and strops. Then you are prepared to do the best work."
- Napoleon LeBlanc, 1895
In my eyes, much the same can be said about any tool, be it knives, razors or whatever.