Crystal Balls are tricky things to make and are made from high-quality optical glass. Because the ball must be flawless many have to be discarded after production. The larger the ball the more likely a flaw can develop, hence the larger sizes are disproportionately more expensive.
Good foam filled in a protective box to minimise the chance of damage. You can see the crystal balls are supplied with a crystal stand, so you can display them on a LED light box for a bit more drama