Cheapest priced copy (The List): $2.49 at Card Kingdom, near mint, their price list as of .
Heartstone 
Artifact · Uncommon · Stronghold · #134
Activated abilities of creatures cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $2.49 to $6.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Premium Deck Series: Slivers | 26 | Uncommon | — | $6.49 |
| The List | H09-26 | Uncommon | $2.49 | — |
| The List | STH-134 | Uncommon | $3.49 | — |
| Stronghold | 134 | Uncommon | $3.49 | — |
5 rulings from Wizards of the Coast
- 4 October 2004It will never reduce any colored mana portion of an activation cost.
- 4 October 2004It will not add a {1} to abilities with no generic mana in their activation cost.
- 4 October 2004The cost reduction can be applied to additional costs.
- 15 July 2006Can’t reduce Snow mana costs.
- 8 June 2016Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.