Cheapest priced copy (Commander 2011): $0.79 at Card Kingdom, near mint, their price list as of .
Scattering Stroke 
Instant · Uncommon · Lorwyn · #82
Counter target spell. Clash with an opponent. If you win, at the beginning of your next main phase, you may add an amount of {C} equal to that spell's mana value. (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 inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.79 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2011 | 60 | Uncommon | $0.79 | — |
| Lorwyn | 82 | Uncommon | $0.79 | $2.99 |
2 rulings from Wizards of the Coast
- 1 October 2007You can't add just some of the mana. You either add all the mana or none of it.
- 1 October 2007You decide whether or not to add that much {C} as the delayed triggered ability resolves at the beginning of your next main phase. You don't decide before then.