Cheapest priced copy (Gatecrash): $3.49 at Card Kingdom, near mint, their price list as of .
Mind Grind 
Sorcery · Rare · Gatecrash · #178
Each opponent reveals cards from the top of their library until they reveal X land cards, then puts all cards revealed this way into their graveyard. X can't be 0.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $3.49 to $9.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Gatecrash | 178 | Rare | $3.49 | $9.99 |
2 rulings from Wizards of the Coast
- 24 January 2013If another spell or ability instructs you to cast Mind Grind “without paying its mana cost,” you won’t be able to. You must pick 0 as the value of X in the mana cost of a spell being cast “without paying its mana cost,” but the X in Mind Grind’s mana cost can’t be 0.
- 24 January 2013If an opponent’s library contains fewer than X land cards, all cards from that library are revealed and put into their graveyard.