Cheapest priced copy (Time Spiral Remastered): $0.79 at Card Kingdom, near mint, their price list as of .
Epic Experiment 
Sorcery · Mythic · Return to Ravnica · #159
Exile the top X cards of your library. You may cast instant and sorcery spells with mana value X or less from among them without paying their mana costs. Then put all cards exiled this way that weren't cast into your graveyard.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.79 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2015 | 216 | Mythic | $0.99 | — |
| Commander 2021 | 216 | Mythic | $0.99 | — |
| Outlaws of Thunder Junction Commander | 222 | Mythic | $0.99 | — |
| Return to Ravnica | 159 | Mythic | $0.99 | $5.99 |
| Time Spiral Remastered | 376 | Special | $0.79 | $3.99 |
5 rulings from Wizards of the Coast
- 19 March 2021If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.
- 19 March 2021You cast the cards one at a time, choosing modes, targets, and so on. The last card you cast will be the first one to resolve.
- 19 March 2021If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 19 March 2021If you can't cast a card, perhaps because there are no legal targets available, or if you choose not to cast it, it will be put into your graveyard.
- 19 March 2021When casting an instant or sorcery card this way, ignore timing restrictions based on the card's type. Other timing restrictions, such as "Cast [this card] only during combat," must be followed.