Cheapest priced copy (Dragons of Tarkir): $0.35 at Card Kingdom, near mint, their price list as of .
Pinion Feast 
Instant · Common · Dragons of Tarkir · #195
Destroy target creature with flying. Bolster 2. (Choose a creature with the least toughness among creatures you control and put two +1/+1 counters on it.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dragons of Tarkir | 195 | Common | $0.35 | $0.49 |
| The List | DTK-195 | Common | $0.35 | — |
3 rulings from Wizards of the Coast
- 25 February 2015You must choose a creature with flying in order to cast Pinion Feast. You can’t cast it without a legal target just to bolster.
- 25 February 2015You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves. That could be the creature with the bolster ability, if it’s still under your control and has the least toughness.
- 25 February 2015Bolster itself doesn’t target any creature, though some spells and abilities that bolster may have other effects that target creatures. For example, you could put counters on a creature with protection from white with Aven Tactician’s bolster ability.