Cheapest priced copy (Duel Decks: Elspeth vs. Kiora): $0.35 at Card Kingdom, near mint, their price list as of .
Celestial Flare 
Instant · Common · Magic Origins · #8
Target player sacrifices an attacking or blocking creature of their choice.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duel Decks: Elspeth vs. Kiora | 4 | Common | $0.35 | — |
| Magic 2014 | 12 | Common | $0.35 | $0.49 |
| Magic Origins | 8 | Common | $0.35 | $0.49 |
| The List | ORI-8 | Common | $0.35 | — |
3 rulings from Wizards of the Coast
- 1 July 2013Celestial Flare targets only a player, not any creature. A creature with hexproof or protection from white can be sacrificed this way.
- 1 July 2013If the player sacrifices a blocking creature, any attacking creature it was blocking remains blocked. Unless that attacking creature has trample or is being blocked by another creature, it won’t assign or deal combat damage.
- 1 July 2013Creatures continue to be attacking or blocking creatures through the end of combat step. It is possible to cast Celestial Flare within combat but after combat damage is dealt (specifically, during the combat damage step or the end of combat step). Only attacking and blocking creatures that survived combat damage can be sacrificed at this time.