Cheapest priced copy (Gatecrash): $0.35 at Card Kingdom, near mint, their price list as of .
Spell Rupture 
Instant · Common · Gatecrash · #52
Counter target spell unless its controller pays {X}, where X is the greatest power among creatures you control.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Gatecrash | 52 | Common | $0.35 | $1.99 |
One ruling from Wizards of the Coast
- 24 January 2013The value of X is the greatest power among creatures you control when Spell Rupture resolves. If you control no creatures at that time, X will be 0. The target spell’s controller can choose to pay {0} (simply by indicating they wish to do so). That player can also choose to not pay {0} and the spell will be countered.