Cheapest priced copy (Conspiracy: Take the Crown): $1.79 at Card Kingdom, near mint, their price list as of .
Wild Pair 
Enchantment · Rare · Planar Chaos · #144
Whenever a creature enters, if you cast it from your hand, you may search your library for a creature card with the same total power and toughness, put it onto the battlefield, then shuffle.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
3 printings · $1.79 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Conspiracy: Take the Crown | 196 | Rare | $1.79 | $3.49 |
| Premium Deck Series: Slivers | 30 | Rare | — | $2.49 |
| Planar Chaos | 144 | Rare | $2.29 | $4.49 |
3 rulings from Wizards of the Coast
- 1 February 2007The game checks the power and toughness of the creature that just entered as it exists on the battlefield. That might mean it's impossible to get another copy of that same card. For example, a Triskelion on the battlefield is 4/4, but a Triskelion in your library is 1/1. The power and toughness might also have been affected while the triggered ability was on the stack (such as with Giant Growth, Sudden Death, or Ovinize).
- 1 February 2007If you cast a 2/2 Grizzly Bears, for example, you may then search for any creature with total power and toughness 4. It can be 0/4, 1/3, 2/2, or 3/1.
- 1 February 2007If the creature that entered has left the battlefield by the time the ability resolves, use the power and toughness of that creature as it last appeared before leaving the battlefield.