If you look around and are informed then you can easily purchase drives that are designed for Nas use. I shucked three eight terabyte Western digital external hard drives and they were all WD reds, but because of the deal they were running they were $60 a piece cheaper inside of the shell than they were outside of the shell.
And most franchises are required to purchase their raw ingredients from the parent corporation, which means that even if they choose to be flexible on their prices their baseline costs are still set by a global conglomerate.