Cheapest priced copy (Outlaws of Thunder Junction Commander): $0.79 at Card Kingdom, near mint, their price list as of .
Diluvian Primordial 
Creature — Avatar · 5/5 · Rare · Gatecrash · #33
Flying
When this creature enters, for each opponent, you may cast up to one target instant or sorcery card from that player's graveyard without paying its mana cost. If a spell cast this way would be put into a graveyard, exile it instead.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.79 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2021 | 120 | Rare | $0.99 | — |
| Game Night: Free-for-All | 26 | Rare | $0.99 | — |
| Gatecrash | 33 | Rare | $0.99 | $4.49 |
| Outlaws of Thunder Junction Commander | 96 | Rare | $0.79 | — |
| The List | GTC-33 | Rare | $0.79 | — |
| Starter Commander Decks | 47 | Rare | $0.79 | — |
9 rulings from Wizards of the Coast
- 24 January 2013If an instant or sorcery card you cast this way is countered, it will still be exiled.
- 24 January 2013If an instant or sorcery card you cast this way goes to a zone other than exile or a graveyard, perhaps because one of its abilities says to put it into its owner's hand, it won't be exiled. This is true even if the card would be put into a graveyard later that turn.
- 24 January 2013If a card has {X} in its mana cost, you must choose 0 as its value.
- 24 January 2013If you cast an instant or sorcery spell with cipher this way, you may exile the card encoded on a creature you control. If you can't, or if you choose not to, the card will end up exiled but not encoded on a creature.
- 24 January 2013You can choose a number of targets up to the number of opponents you have, one target per opponent.
- 24 January 2013When casting an instant or sorcery card this way, ignore timing restrictions based on the card's type. Other timing restrictions, such as "Cast [this card] only during combat," must be followed.
- 24 January 2013You cast the cards one at a time, choosing modes, targets and so on. The last card you cast will be the first one to resolve.
- 24 January 2013If you can't cast one of the target instant or sorcery cards, perhaps because there are no legal targets available, or if you choose not to cast one, it will remain in its owner's graveyard.
- 24 January 2013If you cast a card "without paying its mana cost," you can't pay alternative costs such as overload costs. You can pay additional costs such as kicker costs. If the card has mandatory additional costs, you must pay those.