Cheapest priced copy (Warhammer 40,000 Commander): $5.49 at Card Kingdom, near mint, their price list as of .
Herald's Horn 
Artifact · Uncommon · Jumpstart · #469
As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
16 printings · $5.49 to $16.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Warhammer 40,000 Commander | 241 | Uncommon | $5.49 | — |
| Warhammer 40,000 Commander | 241★ | Uncommon | — | — |
| Commander 2017 | 53 | Uncommon | $5.99 | — |
| Commander Legends: Battle for Baldur's Gate | 862 | Uncommon | $5.49 | — |
| Commander Masters | 953 | Uncommon | $5.49 | — |
| Foundations Commander | 264 | Uncommon | $5.49Out of stock | — |
| Final Fantasy Commander | 228 | Rare | — | $7.49 |
| Jumpstart | 469 | Uncommon | $5.49 | — |
| The Lost Caverns of Ixalan Commander | 304 | Uncommon | $5.49 | — |
| Tales of Middle-earth Commander | 280 | Uncommon | $5.49 | — |
| Modern Horizons 3 Commander | 296 | Uncommon | $5.99 | $13.99 |
| March of the Machine Commander | 360 | Uncommon | $5.49 | — |
| Marvel Super Heroes Commander (Avengers Monitoring Station) | 287 | Uncommon | $5.49 | $6.99 |
| Year of the Tiger 2022 | 5 | Rare | — | $16.99 |
| The List | C17-53 | Uncommon | $5.49 | — |
| Star Trek Commander | 493 | Uncommon | — | — |
6 rulings from Wizards of the Coast
- 25 August 2017If you somehow control a Herald's Horn with no chosen creature type, no spells will cost less to cast, not even creature spells with no creature type. You'll be able to look at the top card of your library at the beginning of each of your upkeeps, but you can never put it into your hand this way, even if it's a creature card with no creature type.
- 25 August 2017You can't choose multiple creature types, such as "Cat Warrior." A Cat Warrior is both a Cat and a Warrior. It's affected by anything that affects either type and unaffected by things that affect non-Cat or non-Warrior creatures.
- 25 August 2017If you don't put the top card of your library into your hand, you put it back on top of your library without revealing it. You'll draw it in that turn's draw step.
- 25 August 2017To 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. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
- 25 August 2017You must choose an existing creature type, such as Vampire or Cat. Card types such as "artifact" can't be chosen.
- 25 August 2017The effect of Herald's Horn reduces only generic mana in a spell's cost. If that cost has no generic mana, the cost isn't reduced.