Cheapest priced copy (Modern Horizons): $0.35 at Card Kingdom, near mint, their price list as of .
Magmatic Sinkhole 
Instant · Uncommon · Modern Horizons 1 Timeshifts · #17
Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Magmatic Sinkhole deals 5 damage to target creature or planeswalker.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Modern Horizons 1 Timeshifts | 17 | Uncommon | — | $0.49 |
| Modern Horizons | 135 | Common | $0.35 | $0.49 |
3 rulings from Wizards of the Coast
- 19 March 2021Delve doesn’t change a spell’s mana cost or mana value. For example, Treasure Cruise’s mana value is 8 even if you exiled three cards to cast it.
- 19 March 2021You can exile cards to pay only for generic mana, and you can’t exile more cards than the generic mana requirement of a spell with delve. For example, you can’t exile more than seven cards from your graveyard to cast Treasure Cruise unless an effect has increased its cost.
- 19 March 2021Because delve isn’t an alternative cost, it can be used in conjunction with alternative costs, such as flashback. It can also be used to pay for additional costs that include generic mana.