I don't know about other brands, but my dog food is $3 a bag more at Petco than it is at Petsmart. Which means if I buy 10 bags at Petco, I spent $30 more than I would have at Petsmart, and my food is $30 a bag at Petsmart.....so I didn't save much money! I'm sure the other brands equal out like that too. I should start buying at Tractor Supply though, the food is the same price there that it is at Petsmart, but I can use my frequent buyer card. So I'd save $30 a year on dog food, I don't go through enough cat food to save on it. But I never have a reason to go to Tractor Supply, so it would be out of my way.
But yeah, Petco has higher prices on most everything. Pets Supply Plus is kinda high on stuff too, they run about equal with Petco around here. And they wanted $35 for an 18" reptile light when I got my dragon. Uh, don't think so! I went to Petland and got a better brand for $12. But the particular Petco that I go to has more knowledgable employees than Petsmart, and thier crickets (for the dragon) are higher quality, don't die as frequently. I don't need much help on the dogs and cats, but I usually have questions on my fish and dragon, and I trust the Petco guys more. Of course, each store is only as good as the employees they have!