Cheapest priced copy (Commander Legends): $0.35 at Card Kingdom, near mint, their price list as of .
Armory of Iroas 
Artifact — Equipment · Uncommon · Journey into Nyx · #158
Whenever equipped creature attacks, put a +1/+1 counter on it.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends | 299 | Common | $0.35 | $0.49 |
| Journey into Nyx | 158 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 10 November 2020If you move Armory of Iroas from one creature to another, any +1/+1 counters on the first creature remain where they are.
- 10 November 2020The +1/+1 counter is put on the equipped creature before combat damage is dealt.