Cheapest priced copy (Commander 2021): $16.99 at Card Kingdom, near mint, their price list as of .
Stinging Study 
Instant · Rare · Commander 2021 · #44
You draw X cards and you lose X life, where X is the mana value of a commander you own on the battlefield or in the command zone.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $16.99 to $23.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2021 | 44 | Rare | $16.99 | — |
| Commander 2021 | 371 | Rare | $17.99 | — |
| Secret Lair Drop | 2481 | Rare | $18.99 | $23.99 |
2 rulings from Wizards of the Coast
- 16 April 2021If your commander is under the control of another player as Stinging Study resolves, it is still on the battlefield and will still be used to determine the value of X.
- 16 April 2021If you own multiple commanders on the battlefield and/or in the command zone, you choose one of them as Stinging Study resolves to determine the value of X.