Spirit Stones
Priam's eyes lit up after hearing this, the Automatons that came from bandits and not from the official stores are normally heavily modified.
They probably possess dangerous weapons, poison, or even self-destruction options in many cases. These weapons and poison were normally much more expensive than the automatons themselves.
Of course, there are also cases where they can be terrible. Their core may be Brass Tier Automaton but their external parts were for Iron Tier Automatons. This is quite common as well since the bandits or renegade manipulators would normally cut the repair costs of their automatons and use parts that were supposed to be for a lower tier.
However, it doesn't always mean that their prices would be lower, they can even be higher if the bandits have really decided to invest in their automatons.