From a manufacturing standpoint if 2 bags are equal in all other ways the smaller bag is cheaper to make simply by the fact that it uses less material.
So the statement is false until you get down to the true miniature level where making something very, very small becomes difficult.
IE; the world's smallest guitar, a mere 10 microns long or about the size of a single blood cell and invisible to the unaided eye, cost far more to make than the most expensive modern guitar.
I had a friend who worked at a company that made micro fasteners. One day they received a nut from another company that was about the size of a grain of sand. It had been sent as a sample of the company's ability to make such a tiny nut.
My friends company took the nut cross drilled it, threaded the hole and made a locking screw to fit then sent it back.