Cheapest priced copy (Marvel Super Heroes Commander): $7.49 at Card Kingdom, near mint, their price list as of .
Helm of the Host 
Legendary Artifact — Equipment · Rare · Dominaria · #217
At the beginning of combat on your turn, create a token that's a copy of equipped creature, except the token isn't legendary. That token gains haste.
Equip {5}
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
10 printings · $7.49 to $32.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Bloomburrow Commander | 276 | Rare | $8.49 | — |
| The Brothers' War Retro Artifacts | 19 | Mythic | $8.49 | $16.99 |
| The Brothers' War Retro Artifacts | 82 | Mythic | $12.99 | $32.99 |
| The Brothers' War Retro Artifacts | 82z | Mythic | — | — |
| Dominaria | 217 | Rare | $8.49 | $15.99 |
| Marvel Super Heroes Commander | 200 | Rare | $7.49 | $11.99 |
| Marvel Super Heroes Commander | 437 | Rare | $9.49 | — |
| Dominaria Promos | 217p | Rare | $8.49 | $16.99 |
| Dominaria Promos | 217s | Rare | — | $19.99 |
| The List | DOM-217 | Rare | $7.99 | — |
8 rulings from Wizards of the Coast
- 27 April 2018Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the chosen creature will also work.
- 27 April 2018If the equipped creature leaves the battlefield before the triggered ability of Helm of the Host resolves, or if there is no equipped creature, no token is created. However, if Helm of the Host leaves the battlefield while its triggered ability is on the stack, a token will be created of the creature it last equipped. If that creature has also left the battlefield, its last known information is used to determine what the token looks like.
- 27 April 2018If the copied creature has {X} in its mana cost, X is considered to be 0.
- 27 April 2018The token isn't legendary, and this exception is copiable. If something else copies the token later, that copy also won't be legendary. If you control two or more permanents with the same name but only one is legendary, the "legend rule" doesn't apply.
- 27 April 2018If the copied creature is copying something else (for example, if the copied creature is a Clone), then the token enters the battlefield as whatever that creature copied.
- 27 April 2018The token copies exactly what was printed on the original creature and nothing else (unless that creature is copying something else or is a token; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.
- 27 April 2018The token gains haste indefinitely, and this effect isn't copiable. If something else copies the token later, that copy won't have haste.
- 27 April 2018If the copied creature is a token, the token that's created copies the original characteristics of that token as stated by the effect that created that token.