Cheapest priced copy (Eternal Masters): $0.35 at Card Kingdom, near mint, their price list as of .
Aven Riftwatcher 
Creature — Bird Rebel Soldier · 2/3 · Common · Planar Chaos · #1
Flying
Vanishing 3 (This creature enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When this creature enters or leaves the battlefield, you gain 2 life.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Eternal Masters | 1 | Common | $0.35 | $0.49 |
| Planar Chaos | 1 | Common | $0.35 | $0.49 |
| The List | PLC-1 | Common | $0.35 | — |
| Time Spiral Remastered | 6 | Common | $0.35 | $0.49 |