I purchase cattle, chicken feed, and a sport fish pond feed currently. If purina already delivers product to them and they are a huge chain store I don't understand the shipping fees one bit. We are talking about tractor supply store.
TSC stores here may sell some Purina products, but they are not what I consider a Purina dealer. With the checkerboard on the sign and all.
A full service Purina dealer would IMHO get you whatever Purina product you want without a delivery charge - they have Purina trucks bringing product to them on a regular schedule. You might have to wait a week or two (like I did for Aquamax 600 early in March), but I would not expect a separate delivery charge.