Cheapest priced copy (Zendikar): $0.35 at Card Kingdom, near mint, their price list as of .
Needlebite Trap 
Instant — Trap · Uncommon · Zendikar · #105
If an opponent gained life this turn, you may pay {B} rather than pay this spell's mana cost.
Target player loses 5 life and you gain 5 life.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Zendikar | 105 | Uncommon | $0.35 | $0.99 |
4 rulings from Wizards of the Coast
- 1 October 2009You may ignore a Trap's alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.
- 1 October 2009Needlebite Trap's alternative cost condition checks only whether life was gained. It doesn't care whether life was also lost. For example, if an opponent gained 4 life and lost 6 life during the turn, that player will have a lower life total than they started the turn with — but you can still cast Needlebite Trap by paying {B}.
- 1 October 2009Casting a Trap by paying its alternative cost doesn't change its mana cost or mana value. The only difference is the cost you actually pay.
- 1 October 2009Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.