Cheapest priced copy (Edge of Eternities): $0.35 at Card Kingdom, near mint, their price list as of .
Starport Security 
Artifact Creature — Robot Soldier · 1/1 · Common · Edge of Eternities · #39
{3}{W}, {T}: Tap another target creature. This ability costs {2} less to activate if you control a creature with a +1/+1 counter on it.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Edge of Eternities | 39 | Common | $0.35 | $0.49 |