They cost 1000g upfront and require 1120g in upkeep per day.
They will be a random humanoid with one or two random genetic traits and a Max Level of 20. Getting them injured or killed will greatly reduce relations with the King. They will have 15-25 randomly distibuted genes.
They can't be used for Breeding, Fusion or rituals either.
When you turn them in you get 500g for every level they gained. Do so before the day rolls over, and you won't have to pay that upkeep.
Also see Soldier