Cheapest priced copy (Commander 2019): $0.35 at Card Kingdom, near mint, their price list as of .
Think Twice 
Instant · Common · Foundations · #315
Draw a card.
Flashback {2}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
17 printings · $0.35 to $159.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2019 | 99 | Common | $0.35 | — |
| Foundations | 165 | Common | $0.35 | $0.49 |
| Foundations | 315 | Common | $0.35 | $0.49 |
| Foundations | 425 | Mythic | — | $22.99 |
| Foundations | 435 | Mythic | — | $159.99Out of stock |
| Innistrad Remastered | 92 | Common | $0.35 | $0.49 |
| Innistrad Remastered | 369 | Common | $0.35 | $0.49 |
| Innistrad | 83 | Common | $0.35 | $0.49 |
| Marvel Super Heroes Commander | 787 | Common | $0.35 | $0.49 |
| Outlaws of Thunder Junction Commander | 119 | Common | $0.35 | — |
| The List | TSP-86 | Common | $0.35 | — |
| Tarkir: Dragonstorm Commander | 168 | Common | $0.35 | — |
| Time Spiral | 86 | Common | $0.39 | $2.49 |
| Time Spiral Remastered | 92 | Common | $0.35 | $0.49 |
| Ultimate Masters | 78 | Common | $0.35 | $0.49 |
| Doctor Who | 220 | Common | $0.35 | $0.49 |
| Doctor Who | 811 | Common | — | $0.99 |
6 rulings from Wizards of the Coast
- 8 November 2024A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.
- 8 November 2024To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.
- 8 November 2024You must still follow any timing restrictions and permissions, including those based on the card's type. For instance, you can cast a sorcery using flashback only when you could normally cast a sorcery.
- 8 November 2024If a card with flashback is put into your graveyard during your turn, you can cast it if it's legal to do so before any other player can take any actions.
- 8 November 2024"Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack."
- 8 November 2024You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.