Cheapest priced copy (Eldritch Moon): $0.35 at Card Kingdom, near mint, their price list as of .
Lunar Force 
Enchantment · Uncommon · Eldritch Moon · #68
When an opponent casts a spell, sacrifice this enchantment and counter that spell.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Eldritch Moon | 68 | Uncommon | $0.35 | $1.49 |
3 rulings from Wizards of the Coast
- 13 July 2016You sacrifice Lunar Force even if the spell’s already been countered, perhaps by the ability of another Lunar Force, or if the spell can’t be countered.
- 13 July 2016You can’t choose not to sacrifice Lunar Force.
- 13 July 2016The spell will be countered even if Lunar Force can’t be sacrificed, most likely because it has already left the battlefield. Casting a spell in response to an opponent’s Lunar Force’s triggered ability is generally a bad idea.