Cheapest priced copy (Commander Legends: Battle for Baldur's Gate): $4.49 at Card Kingdom, near mint, their price list as of .
Earthquake Dragon 
Creature — Elemental Dragon · 10/10 · Rare · Commander Legends: Battle for Baldur's Gate · #228
This spell costs {X} less to cast, where X is the total mana value of Dragons you control.
Flying, trample
{2}{G}, Sacrifice a land: Return this card from your graveyard to your hand.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $4.49 to $11.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends: Battle for Baldur's Gate | 228 | Rare | $4.49 | $5.99 |
| Commander Legends: Battle for Baldur's Gate | 588 | Rare | $7.49 | $6.99 |
| Battle for Baldur's Gate Promos | 228s | Rare | — | $11.99 |
5 rulings from Wizards of the Coast
- 10 June 2022Earthquake Dragon's last ability can be activated only if it is in your graveyard.
- 10 June 2022The total cost to cast Earthquake Dragon is locked in before you pay that cost. For example, if you control three Dragons, each with mana value 4, including one you can sacrifice to add {C}, the total cost of Earthquake Dragon is {2}{G}. Then you can sacrifice the Dragon as you activate mana abilities just before paying the cost.
- 10 June 2022If a permanent has {X} in its mana cost, X is 0 when calculating its mana value.
- 10 June 2022Once a player has announced that they are casting Earthquake Dragon, no player may take actions to try and change the number of Dragons its controller controls before that spell's cost is locked in.
- 10 June 2022If the total mana value of Dragons you control is 14 or greater, Earthquake Dragon costs {G} to cast.