Cheapest priced copy (Innistrad): $0.35 at Card Kingdom, near mint, their price list as of .
Frightful Delusion 
Instant · Common · Innistrad · #57
Counter target spell unless its controller pays {1}. That player discards a card.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Innistrad | 57 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 22 September 2011The player discards a card even if they pay {1}.
- 22 September 2011You must target a spell in order to cast Frightful Delusion. You can’t cast it without a legal target just to make a player discard a card.