That's a huge difference
No mana cost, no card cost, and based on the nature of the deck, something you will see every game before too long
Check for seller references: Whether through MTG reference groups or via reference threads in individual buy, sell, and trade groups, this can give you some insight as to whether a seller is trustworthy
But grading those cards still depends largely on trained professionals examining every scratch, edge, corner, and alignment issue by hand (without transparent insight into the process, of course)
Only costing three ink to play, every time this Ursula sings a song, she can essentially sing it twice and then be placed back in the deck rather than discarded