Sell eggs at the Merchant
The official description confirms that chickens lay eggs and that carried eggs can be sold to the Merchant. Current gameplay video also shows separate Sell All Eggs and Sell All Chickens prompts.
Egg weight varies
A single sale receipt shows Black Eggs at both 11 kg and 5.6 kg. That is direct evidence that an egg name is not enough to predict a fixed weight or value.
Do not budget from one haul
A field report observed heavier mixed batches around $40K–$69K, but composition and weights vary. Record your own sale before treating that range as repeatable.