Cheapest priced copy (Avatar: The Last Airbender): $0.35 at Card Kingdom, near mint, their price list as of .
How to Start a Riot 
Instant — Lesson · Common · Avatar: The Last Airbender · #140
Target creature gains menace until end of turn. (It can't be blocked except by two or more creatures.)
Creatures target player controls get +2/+0 until end of turn.
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1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avatar: The Last Airbender | 140 | Common | $0.35 | $0.49 |