Now, correct me if I'm wrong, but when it comes to things like security robots, or siege robots, or, well any non-sapient construct, technological or magical, maybe I'm just not seeing it, but I'm not seeing any price out there for actually buying one.
Can we get some clarification on that? As fun as the mechanic's drone and the drones from Armory are, it would still be nice to have that answer.
Why would you buy a robot? Just wait until one comes at you then reprogram it in self defense.
There are no rules for that, beyond temporary hijacking via Technomancer spells.
"Why pay a mercenary? Just wait for someone to attack you, then brainwash him into being your follower."
Undead followers are probably the comparison point here. Cost is 1000 per CR, but you are limited in how many you can control, there's a social cost to having them, and only certain classes can have them. So purchased constructs would have to cost more per CR for balance reasons.