Cheapest priced copy (Duel Decks: Elspeth vs. Kiora): $0.49 at Card Kingdom, near mint, their price list as of .
Plasm Capture 
Instant · Rare · Duel Decks: Elspeth vs. Kiora · #55
Counter target spell. At the beginning of your next first main phase, add X mana in any combination of colors, where X is that spell's mana value.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 to $3.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duel Decks: Elspeth vs. Kiora | 55 | Rare | $0.49 | — |
| Dragon's Maze | 91 | Rare | $0.49 | $3.99 |
| Outlaws of Thunder Junction Commander | 237 | Rare | $0.49 | — |
2 rulings from Wizards of the Coast
- 15 April 2013If the countered spell had {X} in its mana cost, include the value chosen for that X when determining how much mana to produce. For example, if you counter a spell that costs {X}{R} with X equal to 5, you'll produce six mana.
- 15 April 2013Your precombat main phase is the main phase that happens immediately after your draw step, not any other main phase.