I agree that there is a certain breaking point on when it is just crazy to buy at a local level, but you should support where you can.
And I'm perfectly willing to do so, if it's within reason. $17 dollars is almost twice as much. I can buy 2 bags for almost the price of one. That $17 can buy me lunch for 2 days, or I can use it towards buying a fish or gas for my car. There is a pet warehouse by me that sells the bags for $29.99. I buy from them more than I buy from online just because it's convenient and it gives me a reason to look at fish. But $40 and you don't even have any fish other than some crappy cichlids and .5" clown loaches, no thank you lol.