Cheapest priced copy (Teenage Mutant Ninja Turtles Eternal): $2.79 at Card Kingdom, near mint, their price list as of .
Coin of Mastery 
Artifact · Rare · Teenage Mutant Ninja Turtles Eternal · #38
Each creature you control enters with an additional +1/+1 counter on it for each mana from an artifact source spent to cast it.
{T}: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $2.79 to $27.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Teenage Mutant Ninja Turtles Eternal | 38 | Rare | $2.79 | $27.99 |