Cheapest priced copy (Urza's Legacy): $0.35 at Card Kingdom, near mint, their price list as of .
Intervene 
Instant · Common · Urza's Legacy · #33
Counter target spell that targets a creature.
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
1 printing · $0.35 to $9.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Urza's Legacy | 33 | Common | $0.35 | $9.99 |
4 rulings from Wizards of the Coast
- 4 October 2004If the spell’s target leaves the battlefield before this spell resolves, Intervene won’t resolve since it no longer targets a spell that targets a creature.
- 4 October 2004If a spell is modal, use the target(s) of the current mode only for this check. Targets for the other modes are never selected.
- 4 October 2004It means “targeting at least one creature” not “exactly one creature”.
- 4 October 2004Intervene can only target a spell that is currently targeting a creature.