Cheapest priced copy (The Brothers' War Retro Artifacts): $2.49 at Card Kingdom, near mint, their price list as of .
Scrap Trawler 
Artifact Creature — Construct · 3/2 · Rare · Commander 2021 · #260
Whenever this creature dies or another artifact you control is put into a graveyard from the battlefield, return to your hand target artifact card in your graveyard with lesser mana value.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
8 printings · $2.49 to $4.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Aether Revolt | 175 | Rare | $3.49 | $4.99 |
| The Brothers' War Retro Artifacts | 49 | Rare | $2.49 | $4.49 |
| The Brothers' War Retro Artifacts | 112 | Rare | $3.49 | $4.99 |
| The Brothers' War Retro Artifacts | 112z | Rare | — | — |
| Commander 2021 | 260 | Rare | $2.79 | — |
| March of the Machine Commander | 373 | Rare | $3.49 | — |
| Aether Revolt Promos | 175 | Rare | — | $3.49 |
| Aether Revolt Promos | 175s | Rare | — | $4.99 |
4 rulings from Wizards of the Coast
- 9 February 2017The target artifact card must have a lesser mana value than the artifact that caused Scrap Trawler's ability to trigger by being put into a graveyard. Use the artifact's mana value as it last existed on the battlefield to determine what may be returned.
- 9 February 2017If an artifact is a copy of another artifact with greater mana value, such as Sculpting Steel copying an artifact with mana value 4, Scrap Trawler's ability can target that artifact card in your graveyard when that artifact is put into your graveyard.
- 9 February 2017While on the battlefield or in a graveyard, {X} in an object's mana cost is 0.
- 9 February 2017If Scrap Trawler and another artifact you control are put into a graveyard at the same time, Scrap Trawler's ability triggers for each of them.