Cheapest priced copy (Avatar: The Last Airbender): $0.35 at Card Kingdom, near mint, their price list as of .
Octopus Form 
Instant — Lesson · Common · Avatar: The Last Airbender · #66
Target creature you control gets +1/+1 and gains hexproof until end of turn. Untap it. (It can't be the target of spells or abilities your opponents control.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avatar: The Last Airbender | 66 | Common | $0.35 | $0.49 |