Cheapest priced copy (Modern Masters 2015): $249.99 at Card Kingdom, near mint, their price list as of .
Mox Opal 
Legendary Artifact · Mythic · Double Masters · #275
Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
7 printings · $249.99 to $1399.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters | 275 | Mythic | $279.99 | $349.99 |
| Double Masters | 362 | Mythic | $349.99 | $449.99 |
| Judge Gift Cards 2019 | 3 | Mythic | — | $379.99 |
| Modern Masters 2015 | 223 | Mythic | $249.99 | $349.99 |
| Kaladesh Inventions | 19 | Special | — | $1399.99 |
| Secret Lair Drop | 1072 | Mythic | — | — |
| Scars of Mirrodin | 179 | Mythic | $249.99 | $599.99 |
One ruling from Wizards of the Coast
- 7 August 2020If you control Mox Opal and one other artifact, then have a second Mox Opal enter the battlefield as your third artifact, you can't activate either one's mana ability before putting one into your graveyard due to the “legend rule.”