They make their money because they breed by the hundred if not, thousand. And they have already made back the costs of the housing system. Subtract the most cost efficient food, water, personal, and you have profit. Even though you are getting them at a great price, each little mouse or rat probably costs the breeder just pennies to nickels to produce. And at the same time you are paying quarters to dollars = HUGE PROFIT. I read the math equations for breeding your own and my brain broke about half way through. I'll likely be ordering in bulk soon.