Cheapest priced copy (Mirage): $329.99 at Card Kingdom, near mint, their price list as of .
Phyrexian Dreadnought 
Artifact Creature — Phyrexian Dreadnought · 12/12 · Rare · Mirage · #315
Trample
When this creature enters, sacrifice it unless you sacrifice any number of creatures with total power 12 or greater.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $329.99 to $799.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Judge Gift Cards 2010 | 3 | Rare | — | $799.99 |
| Mirage | 315 | Rare | $329.99 | — |
5 rulings from Wizards of the Coast
- 4 October 2004Phasing in does not trigger "enters" abilities, so you don't have to sacrifice again if it phases in.
- 4 October 2004The sacrifices are simultaneous, not one at a time.
- 15 July 2007If the Dreadnought is no longer on the battlefield when the triggered ability resolves, you may still choose either option.
- 15 July 2007Reverted to its original wording, this now has an "enters" triggered ability. During resolution of the triggered ability, you choose one option or the other.
- 15 April 2013If you are unable to sacrifice 12 power worth of creatures, then you cannot choose that option; in that case, you must sacrifice Phyrexian Dreadnought.