While not likely to be the single most expensive card in the set, I would expect to see this card up there in discussions for most memorable from Azurite Sea
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of Serah Farron or Crystallized Serah's first abilities)
Update 20-12-22: After 2 months of silence, Ravensburger has gifted us with some news by revealing a new card with a formerly unknown cardtype: Action
This isn't the first Disney Lorcana ability to center around searching the deck, but it's the only one so far to offer such a thorough version, making it a card that everyone should keep their eyes on
I've got quite an extensive history with Selesnya tokens, dating all the way back to the original Commander precons