Cheapest priced copy (Amonkhet): $0.35 at Card Kingdom, near mint, their price list as of .
Supply Caravan 
Creature — Camel · 3/5 · Common · Amonkhet · #30
When this creature enters, if you control a tapped creature, create a 1/1 white Warrior creature token with vigilance.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Amonkhet | 30 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 18 April 2017If you don’t control a tapped creature as Supply Caravan enters the battlefield, its ability doesn’t trigger, even if you can tap a creature right away. If you control no tapped creatures as the ability resolves, nothing happens.
- 18 April 2017If an effect causes Supply Caravan to enter the battlefield tapped, it will satisfy its own triggered ability.