Cheapest priced copy (Commander 2017): $3.49 at Card Kingdom, near mint, their price list as of .
Argentum Armor 
Artifact — Equipment · Rare · Forgotten Realms Commander · #198
Equipped creature gets +6/+6.
Whenever equipped creature attacks, destroy target permanent.
Equip {6}
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
6 printings · $3.49 to $24.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Forgotten Realms Commander | 198 | Rare | $3.99 | — |
| Commander 2014 | 228 | Rare | $4.49 | — |
| Commander 2017 | 202 | Rare | $3.49 | — |
| Game Night: Free-for-All | 113 | Rare | $4.99 | — |
| The List | AFC-198 | Rare | $3.49 | — |
| Scars of Mirrodin | 137 | Rare | $3.99 | $24.99 |
2 rulings from Wizards of the Coast
- 1 January 2011You may target any permanent with the triggered ability, not just one controlled by the defending player. If no other player controls a permanent, you must target one of your own.
- 1 January 2011The second ability triggers and resolves during the declare attackers step. The target permanent will be destroyed before blockers are declared.