Cheapest priced copy (Edge of Eternities Commander): $2.99 at Card Kingdom, near mint, their price list as of .
Cloud Key 
Artifact · Rare · The Brothers' War Retro Artifacts · #12
As this artifact enters, choose artifact, creature, enchantment, instant, or sorcery.
Spells you cast of the chosen type cost {1} less to cast.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
10 printings · $2.99 to $17.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Brothers' War Retro Artifacts | 12 | Rare | $3.99 | $6.99 |
| The Brothers' War Retro Artifacts | 75 | Rare | $5.99 | $10.99 |
| The Brothers' War Retro Artifacts | 75z | Rare | — | — |
| Edge of Eternities Commander | 54 | Rare | $2.99 | — |
| Future Sight | 160 | Rare | $5.49 | $17.99 |
| The List | FUT-160 | Rare | $3.99 | — |
| The Zeta Set | 99 | Uncommon | — | — |
| The Zeta Set | 220 | Uncommon | — | — |
| The Zeta Set | 341 | Uncommon | — | — |
| Time Spiral Remastered | 265 | Rare | $2.99 | $10.99 |
2 rulings from Wizards of the Coast
- 19 March 2021The cost reduction applies only to generic mana in the cost of spells of the chosen type you cast.
- 19 March 2021To 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 Cloud Key's ability). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.