Cheapest priced copy (March of the Machine Commander): $2.49 at Card Kingdom, near mint, their price list as of .
Spell Swindle 
Instant · Rare · The List · #XLN-82
Counter target spell. Create X Treasure tokens, where X is that spell's mana value. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $2.49 to $8.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| March of the Machine Commander | 237 | Rare | $2.49 | — |
| The List | XLN-82 | Rare | $2.49 | — |
| Ixalan Promos | 82p | Rare | $4.49 | $8.99 |
| Ixalan Promos | 82s | Rare | — | $7.99 |
| Ixalan | 82 | Rare | $2.79 | $4.49 |
2 rulings from Wizards of the Coast
- 29 September 2017You may target a spell that can't be countered. When Spell Swindle resolves, the target spell will be unaffected, but you'll still get Treasures.
- 29 September 2017For spells with {X} in their mana costs, use the value chosen for X to determine the spell's mana value.