Cheapest priced copy (Wilds of Eldraine): $0.35 at Card Kingdom, near mint, their price list as of .
Stormkeld Prowler 
Creature — Human Rogue · 2/1 · Common · Wilds of Eldraine · #71
Whenever you cast a spell with mana value 5 or greater, put two +1/+1 counters on this creature.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Wilds of Eldraine | 71 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 1 September 2023If a spell has {X} in its mana cost, use the value chosen for that X to determine the mana value of that spell.