When I had rats just as pets, not even as a food source, even then I found a local supplier of Mazuri food, usually a feed store or something similar and would buy in bulk for much cheaper prices than the typical pet stores. That's always the best bet. Sometimes you can find online suppliers that have good prices, but usually once you tack on that shipping charge that's where it gets ya and is no longer any better of a deal than those pet store prices.