Cheapest priced copy (Outlaws of Thunder Junction Commander): $2.79 at Card Kingdom, near mint, their price list as of .
Smirking Spelljacker 
Creature — Djinn Wizard Rogue · 3/3 · Rare · Outlaws of Thunder Junction Commander · #16
Flash
Flying
When this creature enters, exile target spell an opponent controls.
Whenever this creature attacks, if a card is exiled with it, you may cast the exiled card without paying its mana cost.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $2.79 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Outlaws of Thunder Junction Commander | 16 | Rare | $2.79 | — |
| Outlaws of Thunder Junction Commander | 52 | Rare | $3.49 | — |
5 rulings from Wizards of the Coast
- 12 April 2024If you cast a spell “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the spell has any mandatory additional costs, those must be paid to cast the spell.
- 12 April 2024Spells that can’t be countered can still be exiled by Smirking Spelljacker’s triggered ability. They won’t resolve.
- 12 April 2024If the spell you cast has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 12 April 2024You choose whether to cast the exiled card as Smirking Spelljacker’s last ability resolves. If you do, you do so as part of the resolution of that ability. You can’t wait to cast it later in the turn. Timing restrictions based on the card’s types are ignored.
- 12 April 2024If you cast a card exiled with Smirking Spelljacker, it will go to the stack. From there, it will likely go to the battlefield or back to its owner’s graveyard. Even if it returns to exile, it will no longer be exiled with Smirking Spelljacker, so you can’t cast it again.