Cheapest priced copy (Khans of Tarkir): $0.49 at Card Kingdom, near mint, their price list as of .
Meandering Towershell 
Creature — Turtle · 5/9 · Rare · Secret Lair Drop · #236
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever this creature attacks, exile it. Return it to the battlefield under your control tapped and attacking at the beginning of the declare attackers step on your next turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Khans of Tarkir | 141 | Rare | $0.49 | $0.49 |
| The List | KTK-141 | Rare | $0.49 | — |
| Secret Lair Drop | 236 | Rare | $0.99 | $0.79 |
4 rulings from Wizards of the Coast
- 20 September 2014If Meandering Towershell enters the battlefield attacking, it wasn’t declared as an attacking creature that turn. Abilities that trigger when a creature attacks, including its own triggered ability, won’t trigger.
- 20 September 2014On the turn Meandering Towershell attacks and is exiled, raid abilities will see it as a creature that attacked. Conversely, on the turn Meandering Towershell enters the battlefield attacking, raid abilities will not.
- 20 September 2014As Meandering Towershell returns to the battlefield because of the delayed triggered ability, you choose which opponent or opposing planeswalker it’s attacking. It doesn’t have to attack the same opponent or opposing planeswalker that it was when it was exiled.
- 20 September 2014If you attack with a Meandering Towershell that you don’t own, you’ll control it when it returns to the battlefield.