Cheapest priced copy (Commander 2011): $0.35 at Card Kingdom, near mint, their price list as of .
Punishing Fire 
Instant · Uncommon · Zendikar · #142
Punishing Fire deals 2 damage to any target.
Whenever an opponent gains life, you may pay {R}. If you do, return this card from your graveyard to your hand.
Legal inCommanderLegacyVintage
Banned inModern
Not legal inBrawlStandardPioneerPauper
4 printings · $0.35 to $16.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2011 | 131 | Uncommon | $0.35 | — |
| Duel Decks: Knights vs. Dragons | 66 | Uncommon | $0.49 | — |
| The List | DDG-66 | Uncommon | $0.35 | — |
| Zendikar | 142 | Uncommon | $0.35 | $16.99 |
3 rulings from Wizards of the Coast
- 1 October 2009You choose whether to pay {R} as the triggered ability resolves.
- 1 October 2009If Punishing Fire has left your graveyard by the time its triggered ability resolves, you may still pay {R}, but you won't return it to your hand. This is true even if Punishing Fire has left your graveyard and returned to it by the time its triggered ability resolves.
- 1 October 2009Punishing Fire's triggered ability triggers only if it's already in your graveyard at the time an opponent gains life. For example, you can cast it in response to a spell or ability that will cause an opponent to gain life. In that case, Punishing Fire will resolve first, so it will be in the graveyard by the time the opponent gains life. However, if you wait until an opponent actually gains life and then cast Punishing Fire, you won't be able to return it to your hand at that time.