Cheapest priced copy (Bloomburrow Commander): $0.59 at Card Kingdom, near mint, their price list as of .
Reliant's Betrayal 
Illusionist's Gambit
Instant · Rare · Secret Lair Drop · #2750
Cast this spell only during the declare blockers step on an opponent's turn.
Remove all attacking creatures from combat and untap them. After this phase, there is an additional combat phase. Each of those creatures attacks that combat if able. They can't attack you or planeswalkers you control that combat.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.59 to $0.69 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Bloomburrow Commander | 166 | Rare | $0.59 | — |
| Commander 2013 | 47 | Rare | $0.69 | — |
| Secret Lair Drop (Reliant's Betrayal) | 2750 | Rare | — | — |
| Wilds of Eldraine Commander | 97 | Rare | $0.69 | — |
3 rulings from Wizards of the Coast
- 17 October 2013If there's a cost associated with having a creature attack, the player isn't forced to pay that cost, so it doesn't have to attack.
- 17 October 2013Creatures that didn't attack during the combat phase when Illusionist's Gambit resolved aren't required to attack in the additional combat phase, although they may. Those creatures can attack you or a planeswalker you control.
- 17 October 2013If, during a player's declare attackers step, a creature is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under that player's control continuously since the turn began (and doesn't have haste), then it doesn't attack.