Cheapest priced copy (Urza's Saga): $0.49 at Card Kingdom, near mint, their price list as of .
Child of Gaea 
Creature — Elemental · 7/7 · Rare · Urza's Saga · #242
Trample
At the beginning of your upkeep, sacrifice this creature unless you pay {G}{G}.
{1}{G}: Regenerate this creature.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Urza's Saga | 242 | Rare | $0.49 | — |
2 rulings from Wizards of the Coast
- 4 October 2004You choose whether to pay or not on resolution. If not, then you sacrifice Child of Gaea. You can choose to not pay even if you no longer control Child of Gaea on resolution.
- 1 October 2009If you do choose not to pay, but no longer control Child of Gaea, you cannot sacrifice. It will remain on the battlefield under its current controller’s control.