Cheapest priced copy (Lorwyn): $0.49 at Card Kingdom, near mint, their price list as of .
Broken Ambitions 
Instant · Common · Lorwyn · #54
Counter target spell unless its controller pays {X}. Clash with an opponent. If you win, that spell's controller mills four cards. (Each clashing player reveals the top card of their library, then puts that card on their choice of the top or bottom. A player wins if their card had a greater mana value.)
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.49 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Lorwyn | 54 | Common | $0.49 | $3.49 |
2 rulings from Wizards of the Coast
- 1 October 2007The clash (and the result of the clash if you win) happens regardless of whether the targeted spell was countered or {X} was paid.
- 1 October 2007The opponent you clash with doesn't have to be the controller of the targeted spell.