Cheapest priced copy (Shards of Alara): $0.35 at Card Kingdom, near mint, their price list as of .
Oblivion Ring 
Enchantment · Uncommon · Magic 2013 · #22
When this enchantment enters, exile another target nonland permanent.
When this enchantment leaves the battlefield, return the exiled card to the battlefield under its owner's control.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
12 printings · $0.35 to $5.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Shards of Alara | 20 | Common | $0.35 | $0.49 |
| Archenemy | 3 | Common | $0.39 | — |
| Commander 2011 | 23 | Common | $0.69 | — |
| Duel Decks: Knights vs. Dragons | 34 | Common | $0.59 | — |
| Duel Decks: Venser vs. Koth | 28 | Uncommon | $0.69 | — |
| Friday Night Magic 2009 | 11 | Rare | — | $5.49Out of stock |
| Planechase | 4 | Common | $0.35 | — |
| Lorwyn | 34 | Common | $0.35 | $4.99 |
| Magic 2012 | 27 | Uncommon | $0.35 | $0.79Out of stock |
| Magic 2013 | 22 | Uncommon | $0.35 | $0.79 |
| Modern Masters 2015 | 29 | Uncommon | $0.35 | $0.49 |
| The List | LRW-34 | Common | $0.35 | — |
4 rulings from Wizards of the Coast
- 1 October 2007If Oblivion Ring leaves the battlefield before its first ability has resolved, its second ability will trigger and do nothing. Then its first ability will resolve and exile the targeted nonland permanent forever.
- 1 October 2007If there are no nonland permanents on the battlefield other than an Oblivion Ring, and the card it exiled was another Oblivion Ring, casting a third Oblivion Ring will result in an involuntary infinite loop that will end the game in a draw (unless someone chooses to break it by putting another nonland permanent onto the battlefield or destroying one of the Oblivion Rings, for example).
- 1 October 2008If the exiled card is an Aura, that card’s owner chooses what it will enchant as it comes back onto the battlefield. An Aura put onto the battlefield this way doesn’t target anything, but the Aura’s enchant ability restricts what it can be attached to. If the Aura can’t legally be attached to anything, it remains exiled forever.
- 1 July 2012Auras attached to the exiled permanent will be put into their owners’ graveyards. Equipment attached to the exiled permanent will become unattached and remain on the battlefield. Any counters on the exiled permanent will cease to exist.