Cheapest priced copy (Commander 2021): $0.35 at Card Kingdom, near mint, their price list as of .
Living Lore 
Creature — Avatar · */* · Uncommon · Commander 2021 · #121
As this creature enters, exile an instant or sorcery card from your graveyard.
Living Lore's power and toughness are each equal to the exiled card's mana value.
Whenever this creature deals combat damage, you may sacrifice it. If you do, you may cast the exiled card without paying its mana cost.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2021 | 121 | Uncommon | $0.35 | — |
| Dragons of Tarkir | 61 | Rare | $0.49 | $0.49 |
| Dragons of Tarkir Promos | 61s | Rare | — | $0.49 |
| Ultimate Masters | 62 | Uncommon | $0.35 | $0.49 |
8 rulings from Wizards of the Coast
- 7 December 2018Similarly, if the exiled card somehow leaves exile while Living Lore is on the battlefield, it will become a 0/0 creature.
- 7 December 2018If there are no instant or sorcery cards in your graveyard as Living Lore enters the battlefield, it will enter the battlefield as a 0/0 creature and be put into its owner's graveyard due to having 0 toughness.
- 7 December 2018If 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, such as kicker costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, those must be paid to cast the card.
- 7 December 2018You may cast a sorcery this way even if it's not your turn.
- 7 December 2018If an instant or sorcery spell puts Living Lore onto the battlefield, that spell is still on the stack while you choose a card to exile. You can't exile it with Living Lore.
- 7 December 2018If 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.
- 7 December 2018Living Lore's last ability will trigger whenever it deals combat damage, no matter if that damage is dealt to an opponent, an opposing planeswalker, or a creature it's blocking or being blocked by. You choose whether to sacrifice Living Lore as that ability resolves. If Living Lore has already left the battlefield, perhaps because it was dealt lethal damage at the same time it dealt damage, you can't sacrifice it.
- 7 December 2018If Living Lore leaves the battlefield, the ability that defines its power and toughness will lose track of the exiled card. Its power and toughness are 0 in other zones.