I feel positive that we could find a food she liked just as well for less than half that price, but I’m also positive it wouldn’t be as good for her.
How Much Is Too Much To Pay For Dog Food?
Bea Bischoff

Is it possible that you’re inadvertently influencing their behaviour (e.g., are you fussing over them or giving them more attention in certain circumstances)? I think the Hawthorne effect particularly applies to animals.

Regarding the cost of the dog food, as long as you can afford it, why not? Some people buy expensive German cars and other people buy cheap runabouts. How you spend your money is up to you.