Cheapest priced copy (Outlaws of Thunder Junction Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Feed the Swarm 
Sorcery · Common · Commander 2021 · #144
Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
27 printings · $0.49 to $17.99 at Card Kingdom
3 rulings from Wizards of the Coast
- 8 November 2024If a permanent on the battlefield has {X} in its mana cost, X is 0 for the purpose of determining its mana value.
- 8 November 2024If the target permanent is an illegal target by the time Feed the Swarm tries to resolve, the spell doesn't resolve. You don't lose any life. If the target is legal but not destroyed (most likely because it has indestructible), you do lose life.
- 8 November 2024The amount of life you lose is determined by the permanent's mana value as it last existed on the battlefield.