Cheapest priced copy (Zendikar): $0.49 at Card Kingdom, near mint, their price list as of .
Lavaball Trap 
Instant — Trap · Rare · Zendikar · #135
If an opponent had two or more lands enter the battlefield under their control this turn, you may pay {3}{R}{R} rather than pay this spell's mana cost.
Destroy two target lands. Lavaball Trap deals 4 damage to each creature.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Zendikar | 135 | Rare | $0.49 | $2.49 |
6 rulings from Wizards of the Coast
- 1 October 2009Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.
- 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 2009If both targeted lands are illegal targets by the time Lavaball Trap resolves, the entire spell doesn't resolve. No creatures are dealt damage.
- 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 2009You may target any two lands, not just ones that entered this turn.
- 1 October 2009All creatures are dealt damage, not just ones controlled by the targeted lands' controller(s).