Based on relatively limited research, it seems that the material making up these dice is not aquamarine cat's eye, cat's eye, or even quartz cat's eye. The coloration, hardness, and price are all different from the loose stones that can be found on gemstone storefronts.
My guess is that the high price relative to other acrylic sets is just due to the particular style of the set. In other words, you're paying for perceived aesthetic value and not for material rarity. I could be completely wrong though; I'm admittedly not an expert on precious stones and their synthetic counterparts.