Cheapest priced copy (Fate Reforged): $0.35 at Card Kingdom, near mint, their price list as of .
Ainok Guide 
Creature — Dog Scout · 1/1 · Common · Fate Reforged · #121
When this creature enters, choose one —
• Put a +1/+1 counter on this creature.
• Search your library for a basic land card, reveal it, then shuffle and put that card on top.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fate Reforged | 121 | Common | $0.35 | $0.49 |
| Foundations Jumpstart | 625 | Common | $0.35 | — |
2 rulings from Wizards of the Coast
- 24 November 2014You choose which mode you're using as you put the ability on the stack, after the creature has entered the battlefield. Once you've chosen a mode, you can't change that mode even if the creature leaves the battlefield in response to that ability.
- 24 November 2014If a mode requires a target and there are no legal targets available, that mode can't be chosen. You must choose another mode if able.