Cheapest priced copy (Dominaria United): $0.35 at Card Kingdom, near mint, their price list as of .
Argivian Phalanx 
Creature — Human Kor Soldier · 4/4 · Common · Foundations Jumpstart · #168
Affinity for creatures (This spell costs {1} less to cast for each creature you control.)
Vigilance (Attacking doesn't cause this creature to tap.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United | 5 | Common | $0.35 | $0.49 |
| Foundations Jumpstart | 168 | Common | $0.35 | — |
2 rulings from Wizards of the Coast
- 9 September 2022Argivian Phalanx's first ability can't reduce the {W} in its cost.
- 9 September 2022To 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 Argivian Phalanx). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.