Cheapest priced copy (Tarkir: Dragonstorm): $0.35 at Card Kingdom, near mint, their price list as of .
Stormbeacon Blade 
Artifact — Equipment · Uncommon · Tarkir: Dragonstorm · #27
Equipped creature gets +3/+0.
Whenever equipped creature attacks, draw a card if you control three or more attacking creatures.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Tarkir: Dragonstorm | 27 | Uncommon | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 4 April 2025The second ability checks the number of attacking creatures you control only as the ability resolves. If another attack trigger (such as from the mobilize ability) puts creatures onto the battlefield attacking, you can choose to order the triggered abilities so that those creatures enter before Stormbeacon Blade’s ability resolves.