Cheapest priced copy (Foundations Commander): $1.29 at Card Kingdom, near mint, their price list as of .
Herald of War 
Creature — Angel · 3/3 · Rare · Avacyn Restored · #24
Flying
Whenever this creature attacks, put a +1/+1 counter on it.
Angel spells and Human spells you cast cost {1} less to cast for each +1/+1 counter on this creature.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
4 printings · $1.29 to $7.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Avacyn Restored | 24 | Rare | $2.79 | $7.99 |
| Foundations Commander | 34 | Rare | $1.29 | — |
| Foundations Jumpstart | 207 | Rare | $2.79 | — |
| Midnight Hunt Commander | 86 | Rare | $2.49 | — |
5 rulings from Wizards of the Coast
- 1 May 2012The cost reduction is based on the total number of +1/+1 counters on Herald of War, not just the ones put on it by its own ability.
- 1 May 2012If there are additional costs to cast a creature spell, such as a kicker cost, apply those increases before applying cost reductions.
- 1 May 2012To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.
- 1 May 2012The +1/+1 counter is put on Herald of War before blockers are declared and combat damage is dealt.
- 1 May 2012A creature spell that's both an Angel and a Human will cost {1} less to cast for each +1/+1 counter on Herald of War.