You are leaving out a lot of the total cost of ownership. $30K is the sticker price. You should be calculating the EAC(Equivalent Annual Cost) of the robot. Things like, insurance, energy, maintenance, eventually upgrade/replacement. Remember the labor to fix a robot is much more expensive(probably around 10x with tools and other overhead) than the labor the robot is replacing. I wouldn't say it's definitely cheaper with human labor, but it's far from an obvious difference.