Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Expose Evil 
Instant · Common · Shadows over Innistrad · #19
Tap up to two target creatures.
Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | SOI-19 | Common | $0.35 | — |
| Shadows over Innistrad | 19 | Common | $0.35 | $0.49 |
5 rulings from Wizards of the Coast
- 8 April 2016If an effect refers to a Clue, it means any Clue artifact, not just a Clue artifact token. For example, you can sacrifice Wrench to pay for Alquist Proft, Master Sleuth's activated ability.
- 8 April 2016You can cast Expose Evil with no targets if you only want to investigate.
- 8 April 2016If Expose Evil has at least one target and all of those targets become illegal, the spell doesn't resolve and you won't investigate.
- 8 April 2016You can't sacrifice a Clue to pay multiple costs. For example, you can't sacrifice a Clue token to activate its own ability and also to activate Alquist Proft, Master Sleuth's ability.
- 8 April 2016Clue is an artifact type. Even though it appears on some cards with other permanent types, it's never a creature type, a land type, or anything but an artifact type.