Lava Gecko in Steal an Egg

Lava Gecko hatches from the Lava Gecko Egg, a Rare-rarity egg found in the Volcano. Volcano is zone 6 of 12 on the wiki's Biomes list; the wiki lists its entry requirement as 700K speed, and the nests there are watched by the Cerberus.

The wiki lists its base income as $180/s, which ranks it 8th of the 8 Volcano pets by base rate — Lava Dragon tops the Volcano at $100M/s. Base rate is what a normal-size, un-mutated hatch earns; everything above that comes from the size roll and the colour mutation.

With a colour mutation and no size bonus, the same Lava Gecko would earn roughly: Silver ×1.2 ≈ $216/s, Golden ×2.5 ≈ $450/s, Rainbow ×3.5 ≈ $630/s (multipliers from the wiki's Mutations page; arithmetic is ours). Add a Giant (×3) or Huge (×5) size roll on top and the numbers multiply again.

Hatching it pays a one-off reward of +24k Speed, $18k, and the egg takes 1m to grow in the pen. That reward is the reason low-income eggs are still worth stealing early: the speed bonus is what gets you into the next zone.

A Rare is usually the first egg in a zone that is worth waiting out the 5-minute nest reset for.