When one considers how broken its effect is, they will understand why
Like most Magic: The Gathering cards, the value of Ghostly Prison depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Special Guests)
This action happens after the first strike damage has been done by Shark Shredder
His ability to trade up the value chain, as well as stick with a decent is good, and he also threatens 4 damage each time he attacks
Costco.com sold the 2-pack (one of each variant) for $59.99 with shipping included
Tokens Matter If you can reliably cast Vanguard Suppressor with its squad ability in your token deck, it can certainly find a good home there