Cheapest priced copy (Mirrodin Besieged): $0.35 at Card Kingdom, near mint, their price list as of .
Piston Sledge 
Artifact — Equipment · Uncommon · Mirrodin Besieged · #124
When this Equipment enters, attach it to target creature you control.
Equipped creature gets +3/+1.
Equip—Sacrifice an artifact.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 124 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 1 June 2011You can sacrifice Piston Sledge to pay its own equip cost. It won't become attached as it will be in your graveyard.
- 1 June 2011If there are no creatures on the battlefield that Piston Sledge could be attached to when its "enters" triggered ability resolves, it remains on the battlefield unattached.