You're comparing probably the most expensive mass market flour (King Arthur) with probably about the cheapest (Walmart's). A 2x-3x price differential sounds about right.
The original flour we were thinking of buying was https://www.webstaurantstore.com/all-purpose-flour-50-lb/104... $12.25/bag (50lb), mildly cheaper than the Sam's Club price above. But then adding in shipping on a truck from PA added another $9.40/bag.
In places where people can easily buy individual 25lb bags for $6.50, though, you don't need to organize a group buy!
