Cheapest priced copy (Avacyn Restored): $0.35 at Card Kingdom, near mint, their price list as of .
Tormentor's Trident 
Artifact — Equipment · Uncommon · Avacyn Restored · #222
Equipped creature gets +3/+0 and attacks each combat if able.
Equip {3}
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 222 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 1 May 2012You still decide which player or planeswalker the equipped creature attacks.
- 1 May 2012If, during your declare attackers step, the equipped creature is tapped, is affected by a spell or ability that says it can’t attack, or hasn’t been under your control continuously since the turn began (and doesn’t have haste), then it doesn’t attack. If there’s a cost associated with having a creature attack, you’re not forced to pay that cost, so it doesn’t have to attack in that case either.