Why does the price jump so much between the smaller size and larger size Akoya pearls?

Because the Akoya pearl mollusk is approximately 3 inches across, large Akoya pearls are very rare. In order to create a large pearl, pearl farmers have to implant the mollusk with a very large bead. Very few of the small shells of the Akoya pearl mollusks are able to handle a large bead and produce larger Akoya pearls.