Cheapest priced copy (Duel Decks: Izzet vs. Golgari): $0.49 at Card Kingdom, near mint, their price list as of .
Galvanoth 
Creature — Beast · 3/3 · Rare · Mirrodin Besieged · #62
At the beginning of your upkeep, you may look at the top card of your library. You may cast it without paying its mana cost if it's an instant or sorcery spell.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duel Decks: Izzet vs. Golgari | 10 | Rare | $0.49 | — |
| Mirrodin Besieged | 62 | Rare | $0.49 | $0.49 |
4 rulings from Wizards of the Coast
- 1 June 2011You may pay additional costs, such as kicker costs, of the instant or sorcery card.
- 1 June 2011If the card has an X in its mana cost, you must choose 0 as its value.
- 1 June 2011If the card you look at isn’t an instant or sorcery card, it remains on top of your library. You don’t reveal it.
- 1 June 2011If the card has any mandatory additional costs, as Kuldotha Rebirth does, you must pay them in order to cast the spell.