Cheapest priced copy (Avacyn Restored): $0.35 at Card Kingdom, near mint, their price list as of .
Unhallowed Pact 
Enchantment — Aura · Common · Avacyn Restored · #124
Enchant creature
When enchanted creature dies, return that card to the battlefield under your control.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 124 | Common | $0.35 | $0.49 |
| Conspiracy | 131 | Common | $0.35 | $0.49 |
| Duel Decks: Nissa vs. Ob Nixilis | 64 | Common | $0.35 | — |
2 rulings from Wizards of the Coast
- 1 May 2012The card will return to the battlefield under your control only if it’s still in the graveyard when Unhallowed Pact’s ability resolves. If it’s not (perhaps because an ability like undying has already returned it to the battlefield), nothing happens.
- 1 May 2012If Unhallowed Pact is enchanting a token creature, that creature can’t return to the battlefield.