Cheapest priced copy (Commander 2018): $0.49 at Card Kingdom, near mint, their price list as of .
Echo Storm 
Sorcery · Rare · March of the Machine Commander · #221
When you cast this spell, copy it for each time you've cast your commander from the command zone this game. You may choose new targets for the copies.
Create a token that's a copy of target artifact.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2018 | 7 | Rare | $0.49 | — |
| March of the Machine Commander | 221 | Rare | $0.49 | — |
11 rulings from Wizards of the Coast
- 13 July 2018If the copied artifact is copying something else (for example, if the copied artifact is a Sculpting Steel), then the token enters the battlefield as whatever that artifact copied.
- 13 July 2018The token copies exactly what was printed on the original artifact and nothing else (unless that artifact is copying something else or is a token; see below). It doesn't copy whether that artifact is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its types, color, or so on.
- 13 July 2018Each Storm's triggered ability can copy the Storm spell even if that spell is countered before that ability resolves.
- 13 July 2018The copies are created on the stack, so they're not “cast.” Abilities that trigger when a player casts a spell (such as the Storm's ability itself) won't trigger.
- 13 July 2018If the copied artifact is a token, the token that's created copies the original characteristics of that token as stated by the effect that created the token.
- 13 July 2018Each copy resolves one at a time. Any abilities that trigger on the artifact token entering the battlefield resolve before the next copy resolves. The original spell is the last to resolve.
- 13 July 2018If the copied artifact has {X} in its mana cost, X is considered to be 0.
- 13 July 2018Each Storm's triggered ability counts only how many times you've cast your commander from the command zone before that triggered ability resolves. If you cast your commander again later, you won't get another copy.
- 13 July 2018Any enters-the-battlefield abilities of the copied artifact will trigger when the token enters the battlefield. Any “as [this artifact] enters the battlefield” or “[this artifact] enters the battlefield with” abilities of the chosen artifact will also work.
- 13 July 2018If your commander was countered, that time you cast it still counts.
- 5 October 2018If you have multiple commanders, you'll copy this spell for each time you've cast either of them. For example, if you've cast one commander once and one twice, you'll copy this spell three times.