Cheapest priced copy (Commander 2013): $1.29 at Card Kingdom, near mint, their price list as of .
Act of Authority 
Enchantment · Rare · Commander 2013 · #1
When this enchantment enters, you may exile target artifact or enchantment.
At the beginning of your upkeep, you may exile target artifact or enchantment. If you do, its controller gains control of this enchantment.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $1.29 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2013 | 1 | Rare | $1.29 | — |
2 rulings from Wizards of the Coast
- 17 October 2013For either ability, if you are the only player who controls an artifact or enchantment, you must choose one of them as the target. However, you may choose to not exile it when the ability resolves.
- 17 October 2013If you choose to not exile a permanent with the second ability, you'll retain control of Act of Authority.