Cheapest priced copy (Modern Masters 2015): $0.49 at Card Kingdom, near mint, their price list as of .
Argent Sphinx 
Creature — Sphinx · 4/3 · Rare · Scars of Mirrodin · #28
Flying
Metalcraft — {U}: Exile this creature. Return it to the battlefield under your control at the beginning of the next end step. Activate only if you control three or more artifacts.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Modern Masters 2015 | 41 | Rare | $0.49 | $0.79 |
| Scars of Mirrodin | 28 | Rare | $0.69 | $0.49 |
3 rulings from Wizards of the Coast
- 1 January 2011If you activate Argent Sphinx’s metalcraft ability during a turn’s end step, Argent Sphinx will return to the battlefield at the beginning of the following turn’s end step.
- 1 January 2011If you control an Argent Sphinx owned by another player and activate its ability, Argent Sphinx will return to the battlefield under your control at the beginning of the next end step. You’ll retain control of it indefinitely.
- 1 January 2011If you activate Argent Sphinx’s metalcraft ability, Argent Sphinx will return to the battlefield at the beginning of the next end step no matter how many artifacts you control at that time.