Cheapest priced copy (Zendikar Rising Commander): $0.35 at Card Kingdom, near mint, their price list as of .
Stinkdrinker Bandit 
Creature — Goblin Rogue · 2/1 · Uncommon · Morningtide · #80
Prowl {1}{B} (You may cast this for its prowl cost if you dealt combat damage to a player this turn with a Goblin or Rogue.)
Whenever a Rogue you control attacks and isn't blocked, it gets +2/+1 until end of turn.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Morningtide | 80 | Uncommon | $0.39 | $1.99 |
| Zendikar Rising Commander | 55 | Uncommon | $0.35 | — |
2 rulings from Wizards of the Coast
- 1 April 2008This ability triggers after blockers are declared during the declare blockers step. Each attacking Rogue you control gets +2/+1 if no creatures were assigned to block it. That creature will get the bonus even if an effect causes it to become blocked.
- 15 April 2013An ability that triggers when something “attacks and isn’t blocked” triggers in the declare blockers step after blockers are declared if (1) that creature is attacking and (2) no creatures are declared to block it. It will trigger even if that creature was put onto the battlefield attacking rather than having been declared as an attacker in the declare attackers step.