Cheapest priced copy (Aether Revolt): $0.35 at Card Kingdom, near mint, their price list as of .
Crackdown Construct 
Artifact Creature — Construct · 2/2 · Uncommon · The List · #AER-148
Whenever you activate an ability of an artifact or creature that isn't a mana ability, this creature gets +1/+1 until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Aether Revolt | 148 | Uncommon | $0.35 | $1.49 |
| The List | AER-148 | Uncommon | $0.35 | — |
4 rulings from Wizards of the Coast
- 9 February 2017An ability whose cost is simply {0} can be activated as many times as you'd like. Each activation causes Crackdown Construct's ability to trigger.
- 9 February 2017Crackdown Construct's ability doesn't trigger if you activate an ability of an artifact or creature card not on the battlefield.
- 9 February 2017An activated mana ability is one that could add mana as it resolves, doesn't have a target, and isn't a loyalty ability.
- 9 February 2017Activated abilities are written in the form "Cost: Effect." Some keyword abilities, such as equip and crew, are activated abilities and will have colons in their reminder texts.