Cheapest priced copy (Dominaria United): $0.35 at Card Kingdom, near mint, their price list as of .
Academy Wall 
Creature — Wall · 0/5 · Common · Dominaria United · #41
Defender
Whenever you cast an instant or sorcery spell, you may draw a card. If you do, discard a card. This ability triggers only once each turn.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United | 41 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 9 September 2022An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. The ability resolves even if that spell is countered.
- 9 September 2022You draw a card and discard a card while Academy Wall's last ability is resolving. No player may take actions between those events, and nothing can happen.