A card's monetary value is typically determined by its demand from players - the more people want it for their decks, the higher its price will go
To recap, this deck is red, white, and green, and led by Kaust, Eyes of the GladeKaust, Eyes of the Glade, a 2/2 Dryad Detective that costs two mana
There's only a short preorder window, so you'll want to mark your calendars if you're clamouring for these
In addition to potentially allowing you to cast an opponent's strongest spells for free, Tasha's static ability creates 3/3 Demon tokens whenever you cast a spell you don't own, converting these stolen spells into additional manpower
Note that you and your opponent can both have Nissa, Steward of Elements in play, but you and your opponent cannot have more than one of them on your respective sides of the battlefield