Cheapest priced copy (Dragons of Tarkir): $0.35 at Card Kingdom, near mint, their price list as of .
Stormrider Rig 
Artifact — Equipment · Uncommon · Dragons of Tarkir · #245
Equipped creature gets +1/+1.
Whenever a creature you control enters, you may attach this Equipment to it.
Equip {2}
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dragons of Tarkir | 245 | Uncommon | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 25 February 2015If the creature that entered the battlefield is no longer on the battlefield as Stormrider Rig's second ability resolves, Stormrider Rig doesn't move. This is also true if that creature can't legally be equipped by Stormrider Rig.