Cheapest priced copy (Throne of Eldraine): $0.99 at Card Kingdom, near mint, their price list as of .
The Circle of Loyalty 
Legendary Artifact · Mythic · Throne of Eldraine · #336
Affinity for Knights (This spell costs {1} less to cast for each Knight you control.)
Creatures you control get +1/+1.
Whenever you cast a legendary spell, create a 2/2 white Knight creature token with vigilance.
{3}{W}, {T}: Create a 2/2 white Knight creature token with vigilance.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.99 to $13.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United Commander | 98 | Mythic | $1.29 | — |
| Throne of Eldraine | 9 | Mythic | $0.99 | $1.49 |
| Throne of Eldraine | 336 | Mythic | $2.99 | $13.99 |
| Jumpstart 2022 | 166 | Mythic | $1.29 | — |
| Throne of Eldraine Promos | 9p | Mythic | $2.79Out of stock | $2.99 |
| Throne of Eldraine Promos | 9s | Mythic | — | $3.99Out of stock |
5 rulings from Wizards of the Coast
- 4 October 2019The Circle of Loyalty's triggered ability won't trigger when you cast it because it's not on the battlefield yet.
- 4 October 2019The cost reduction ability reduces only the generic mana in the relic's cost. The colored mana must still be paid.
- 4 October 2019The Circle of Loyalty's triggered ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
- 4 October 2019To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
- 4 October 2019Once you announce that you're casting a spell, no player may take actions until the spell has been paid for. Notably, opponents can't try to change by how much a relic's cost is reduced.