Cheapest priced copy (Worldwake): $0.35 at Card Kingdom, near mint, their price list as of .
Slingbow Trap 
Instant — Trap · Uncommon · Worldwake · #111
If a black creature with flying is attacking, you may pay {G} rather than pay this spell's mana cost.
Destroy target attacking creature with flying.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Worldwake | 111 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 1 March 2010An “attacking creature” is one that has been declared as an attacker this combat, or one that was put onto the battlefield attacking this combat. Unless that creature leaves combat, it continues to be an attacking creature through the end of combat step, even if the player it was attacking has left the game, or the planeswalker it was attacking has left combat.
- 1 March 2010If you cast Slingbow Trap for {G}, you may target any attacking creature with flying, not just a black one.