Like most Magic: The Gathering cards, the value of Celestial Archon 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 (Theros)
You will always get an opportunity in Innistrad to look awesome fighting off nasty beasties. And lastly, what inspired the incredible showcase art
In most cases, I will be referencing CGCs standards in this guide
For Lost Caverns, those cards will include merfolk creature Lord of Atlantis and the Mana Crypt artifact
Having a Magic: The Gathering card gets banned is a big deal, especially in a format like Commander, where every card Magic has ever printed is available for play
Normally I would say something like when you want to steel a guy you should go for the cheapest and most reliable option in Control Magic and not risk having it undone with something as simple as a Firebolt just for the sake of a 2/2 flier