Cheapest priced copy (Core Set 2021): $0.49 at Card Kingdom, near mint, their price list as of .
Stormwing Entity 
Creature — Elemental · 3/3 · Rare · Core Set 2021 Promos · #73p
This spell costs {2}{U} less to cast if you've cast an instant or sorcery spell this turn.
Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When this creature enters, scry 2.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Core Set 2021 | 73 | Rare | $0.49 | $0.49 |
| Core Set 2021 | 354 | Rare | $0.79 | $0.79Out of stock |
| Core Set 2021 Promos | 73p | Rare | $0.49 | $0.79 |
| Core Set 2021 Promos | 73s | Rare | — | $0.99 |
3 rulings from Wizards of the Coast
- 23 June 2020Stormwing Entity's cost reduction applies just once, no matter how many instant and sorcery spells you've cast this turn.
- 23 June 2020Stormwing Entity's cost reduction applies even if the instant or sorcery spell you cast was countered or didn't resolve.
- 23 June 2020To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Stormwing Entity). The mana value of the spell remains unchanged, no matter what the total cost to cast it was.