Cheapest priced copy (The Hobbit): $0.35 at Card Kingdom, near mint, their price list as of .
Vow to Erebor 
Instant · Common · The Hobbit · #31
Untap target creature you control. It gets +2/+2 until end of turn. If it's a Dwarf, you may attach an Equipment you control to it.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Hobbit | 31 | Common | $0.35 | $0.49 |