Cheapest priced copy (Duskmourn: House of Horror Commander): $0.99 at Card Kingdom, near mint, their price list as of .
Skaab Ruinator 
Creature — Zombie Horror · 5/6 · Mythic · Innistrad · #77
As an additional cost to cast this spell, exile three creature cards from your graveyard.
Flying
You may cast this card from your graveyard.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.99 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duskmourn: House of Horror Commander | 128 | Mythic | $0.99 | — |
| Innistrad | 77 | Mythic | $0.99 | $2.99 |
2 rulings from Wizards of the Coast
- 22 September 2011Skaab Ruinator is on the stack when you pay its costs. It can't be exiled to pay for itself.
- 22 September 2011You must exile three creature cards from your graveyard no matter what zone you're casting Skaab Ruinator from.