Cheapest priced copy (Tarkir: Dragonstorm Commander): $5.99 at Card Kingdom, near mint, their price list as of .
Hellkite Courser 
Creature — Dragon · 6/5 · Mythic · Commander Legends · #666
Flying
When this creature enters, you may put a commander you own from the command zone onto the battlefield. It gains haste. Return it to the command zone at the beginning of the next end step.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $5.99 to $199.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends | 183 | Mythic | $6.99 | $15.99 |
| Commander Legends | 666 | Mythic | $20.99 | $199.99 |
| Tarkir: Dragonstorm Commander | 218 | Mythic | $5.99 | — |
2 rulings from Wizards of the Coast
- 10 November 2020Putting your commander onto the battlefield this way isn't the same as casting that commander. The "commander tax" won't increase.
- 10 November 2020You'll return the commander to the command zone only if it's still on the battlefield as the delayed triggered ability resolves. If it's in another zone, it will stay where it is.