Cheapest priced copy (Alara Reborn): $0.35 at Card Kingdom, near mint, their price list as of .
Demonspine Whip 
Artifact — Equipment · Uncommon · Alara Reborn · #39
{X}: Equipped creature gets +X/+0 until end of turn.
Equip {1}
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Alara Reborn | 39 | Uncommon | $0.35 | $0.49 |
3 rulings from Wizards of the Coast
- 1 May 2009Once Demonspine Whip’s ability resolves and gives the +X/+0 bonus to a creature, that bonus stays with that creature for the rest of the turn even if Demonspine Whip moves to another creature or leaves the battlefield.
- 1 May 2009If Demonspine Whip is no longer on the battlefield by the time its first ability resolves, the game checks whether it was attached to a creature at the time it left the battlefield. If it was, that creature gets the +X/+0 bonus. If it wasn’t, no creature gets the bonus.
- 1 May 2009When the first ability resolves, the +X/+0 bonus is given to the creature that Demonspine Whip is attached to at that time, regardless of what creature (if any) it was attached to when the ability was activated. If Demonspine Whip is on the battlefield but not attached to a creature at this time, no creature gets the bonus.