Cheapest priced copy (Commander Anthology Volume II): $4.49 at Card Kingdom, near mint, their price list as of .
Dualcaster Mage 
Creature — Human Wizard · 2/2 · Rare · Commander Anthology Volume II · #94
Flash
When this creature enters, copy target instant or sorcery spell. You may choose new targets for the copy.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
11 printings · $4.49 to $42.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters | 124 | Rare | $4.99 | $12.99 |
| Commander 2014 | 34 | Rare | $5.49 | — |
| Commander 2020 | 150 | Rare | $4.99 | — |
| Commander 2021 | 165 | Rare | $4.99 | — |
| Commander Anthology Volume II | 94 | Rare | $4.49 | — |
| Commander Legends | 412 | Rare | $4.49 | — |
| Archenemy: Nicol Bolas | 46 | Rare | $4.99Out of stock | — |
| Eternal Masters | 127 | Rare | $4.49 | $15.99 |
| Judge Gift Cards 2015 | 6 | Rare | — | $42.99 |
| Jumpstart | 313 | Rare | $4.49 | — |
| Special Guests | 153 | Mythic | $10.99 | $22.99 |
7 rulings from Wizards of the Coast
- 8 June 2016Dualcaster Mage's triggered ability can target (and copy) any instant or sorcery spell, not just one with targets. It doesn't matter who controls it.
- 8 June 2016If the copy says that it affects "you," it affects the controller of the copy, not the controller of the original spell. Similarly, if the copy says that it affects an "opponent," it affects an opponent of the copy's controller, not an opponent of the original spell's controller.
- 8 June 2016If the spell is modal (that is, it says "Choose one —" or the like), the copy will have the same mode. You can't choose a different one.
- 8 June 2016As Dualcaster Mage's triggered ability resolves, it creates a copy of a spell on the stack. The copy isn't cast, so abilities that trigger when a player casts a spell won't trigger.
- 8 June 2016The copy will have the same targets as the spell it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).
- 8 June 2016You can't choose to pay any additional costs for the copy. However, effects based on any additional or alternative costs paid for the targeted spell are copied as though those same costs were paid for the copy.
- 8 June 2016If the spell has an X whose value was determined as it was cast (like Earthquake does), the copy has the same value of X.