Cheapest priced copy (Core Set 2021): $0.49 at Card Kingdom, near mint, their price list as of .
Idol of Endurance 
Artifact · Rare · Core Set 2021 Promos · #23p
When this artifact enters, exile all creature cards with mana value 3 or less from your graveyard until this artifact leaves the battlefield.
{1}{W}, {T}: Until end of turn, you may cast a creature spell from among cards exiled with this artifact without paying its mana cost.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $0.59 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Core Set 2021 | 23 | Rare | $0.49 | $0.49 |
| Core Set 2021 | 342 | Rare | $0.49 | $0.49 |
| Core Set 2021 Promos | 23p | Rare | $0.49 | $0.49 |
| Core Set 2021 Promos | 23s | Rare | — | $0.59 |
6 rulings from Wizards of the Coast
- 23 June 2020If a card in a player's graveyard has {X} in its mana cost, X is considered to be 0.
- 23 June 2020The last ability of Idol of Endurance doesn't change when you may cast those creature spells. Normally this means during your main phase while the stack is empty, but you can cast a creature spell with flash at other times.
- 23 June 2020If you cast a spell with Idol of Endurance's last ability, it becomes a new object. If it returns to exile, it's no longer exiled with Idol of Endurance, and won't be returned to your graveyard once Idol of Endurance leaves the battlefield.
- 23 June 2020If you cast a spell “without paying its mana cost,” you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
- 23 June 2020If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 23 June 2020The exiled cards return to your graveyard immediately after Idol of Endurance leaves the battlefield. Any cards that had left exile before then (most likely because they were cast with Idol of Endurance's second ability) remain in their current zone.