Cheapest priced copy (Phyrexia: All Will Be One Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Wurmquake 
Sorcery · Rare · Phyrexia: All Will Be One Commander · #57
Corrupted — Create an X/X green Phyrexian Wurm creature token with trample and toxic 1, where X is the amount of mana spent to cast this spell. Then for each opponent with three or more poison counters, you create another one of those tokens.
Flashback {8}{G}{G} (You may cast this card from your graveyard for its flashback cost. Then exile it.)
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.49 to $0.69 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Phyrexia: All Will Be One Commander | 19 | Rare | $0.49 | — |
| Phyrexia: All Will Be One Commander | 57 | Rare | $0.69 | — |
8 rulings from Wizards of the Coast
- 4 February 2023You can't choose to spend more mana to cast Wurmquake than you're asked to just to make a bigger Wurm. In most cases, it's a 6/6 Phyrexian Wurm the first time, and a 10/10 Phyrexian Wurm when you cast Wurmquake with flashback. However, if there are any additional costs to cast it, the mana spent to pay those costs counts.
- 4 February 2023A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.
- 4 February 2023"Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack."
- 4 February 2023If a card with flashback is put into your graveyard during your turn, you can cast it if it's legal to do so before any other player can take any actions.
- 4 February 2023The first token that Wurmquake creates as it resolves is created and enters the battlefield before the rest of them, then you create a number of tokens equal to the number of opponents with three of more poison counters and they enter the battlefield at the same time.
- 4 February 2023You must still follow any timing restrictions and permissions, including those based on the card's type. For instance, you can cast a sorcery using flashback only when you could normally cast a sorcery.
- 4 February 2023You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.
- 4 February 2023To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.