Cheapest priced copy (Commander 2015): $0.35 at Card Kingdom, near mint, their price list as of .
Mystic Retrieval 
Sorcery · Uncommon · Ultimate Masters · #66
Return target instant or sorcery card from your graveyard to your hand.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
7 printings · $0.35 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2015 | 98 | Uncommon | $0.35 | — |
| Commander 2019 | 90 | Uncommon | $0.35 | — |
| Dark Ascension | 42 | Uncommon | $0.35 | $3.49 |
| Innistrad Remastered | 77 | Uncommon | $0.35 | $0.49 |
| Innistrad Remastered | 363 | Uncommon | $3.49 | $3.49 |
| The List | INR-77 | Uncommon | — | — |
| Ultimate Masters | 66 | Uncommon | $0.35 | $0.49 |
7 rulings from Wizards of the Coast
- 22 January 2011Mystic Retrieval can't target itself. It's on the stack when you choose its target.
- 19 March 2021If 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.
- 19 March 2021A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.
- 19 March 2021"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."
- 19 March 2021You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.
- 19 March 2021To 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.
- 19 March 2021You 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.