Cheapest priced copy (Conspiracy): $0.35 at Card Kingdom, near mint, their price list as of .
Vent Sentinel 
Creature — Elemental · 2/4 · Common · Rise of the Eldrazi · #171
Defender
{1}{R}, {T}: This creature deals damage to target player or planeswalker equal to the number of creatures you control with defender.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
4 printings · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Conspiracy | 156 | Common | $0.35 | $0.49 |
| Iconic Masters | 153 | Common | $0.35 | $0.79 |
| The List | IMA-153 | Common | $0.35 | — |
| Rise of the Eldrazi | 171 | Common | $0.35 | $0.49 |