Cheapest priced copy (Commander Masters): $0.79 at Card Kingdom, near mint, their price list as of .
Oath of Jace 
Legendary Enchantment · Rare · Oath of the Gatewatch · #60
When Oath of Jace enters, draw three cards, then discard two cards.
At the beginning of your upkeep, scry X, where X is the number of planeswalkers you control.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.79 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 854 | Rare | $0.79 | — |
| Oath of the Gatewatch | 60 | Rare | $0.79 | $2.49 |
| Oath of the Gatewatch Promos | 60s | Rare | — | $2.49 |
4 rulings from Wizards of the Coast
- 22 January 2016Each of the Oaths is legendary: if you control more than one of any particular Oath, you choose one to remain on the battlefield and the others are put into your graveyard.
- 22 January 2016If you control no planeswalkers as the last ability resolves, you won’t scry at all. Abilities that trigger whenever you scry won’t trigger.
- 22 January 2016The “legend rule” checks the full names of legendary permanents. You can control Oath of Gideon and Oath of Chandra at the same time, for example.
- 22 January 2016Even if you control a particular Oath, you can cast another of that Oath to take advantage of its enters-the-battlefield ability. It will enter the battlefield, causing its first ability to trigger. You will then choose one to keep, as detailed above, and then its enters-the-battlefield ability will resolve.