Cheapest priced copy (Darksteel): $2.29 at Card Kingdom, near mint, their price list as of .
Heartseeker 
Artifact — Equipment · Rare · Darksteel · #124
Equipped creature gets +2/+1 and has "{T}, Unattach Heartseeker: Destroy target creature."
Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $2.29 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Darksteel | 124 | Rare | $2.29 | $5.99 |
3 rulings from Wizards of the Coast
- 1 December 2004“Unattach Heartseeker” means just that — Heartseeker moves off the creature it was equipping and remains on the battlefield.
- 1 December 2004Heartseeker grants an ability to the equipped creature. The ability can target a creature with protection from artifacts (unless the equipped creature is an artifact creature).
- 1 December 2004The equipped creature’s controller chooses whether or not to activate the activated ability. It doesn’t matter who controls Heartseeker.