Several costs come to mind.
First – and strategically significant – is the loss of trust. The tarnishing of image.

Trust is important when it comes to safety. When the safety risk is imposed by a faulty “safety feature”, then importance is increased exponentially.

Second, sound management is something which ought to be able to be assumed at this level in crucial decisions. Instead we see a glaring example of poor contract management – with contractors failing to use attention-capturing, high/impact language required by the Recall Notice. Indeed, call-centre staff are cited as describing the recall as merely precautionary!
The third compounder is a failure to understand risk management. Especially, risk communication. There are decades of lessons around risk communication which emphasise fundamental principles – such as respect and transparency. Principles which appear to have not informed the approach adopted by Mercedes.
The $12.5m fine may be the least of the costs