Like most Pokmon cards, the value of Celebi 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 (Mega Evolution)
Look closer and see a result that is a couple things away from Sire of Seven Deaths
It only gets the creature to your hand, but the possibility of getting rid of a pesky planeswalker or creature seems like a good trade to me
The basic version of what I like to call an overly enthusiastic chocobo is only around $40, but if you want nice matching borders, or any color that isn't yellow, then you better hope your pockets are deep
And dont sleep on cards like Choice of Damnations, Hell's Caretaker, Sorrow's Path, Inverter of Truth, or In the Eye of Chaos