Cheapest priced copy (Murders at Karlov Manor): $0.35 at Card Kingdom, near mint, their price list as of .
Thinking Cap 
Artifact — Equipment · Common · Murders at Karlov Manor · #257
Equipped creature gets +1/+2.
Equip Detective {1}
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Murders at Karlov Manor | 257 | Common | $0.35 | $0.49 |