Why would there be much labor? Cameras aren't mounted in the dashboard
The monitors are (I quote you: "and that's including the monitor!"). You want the camera without a monitor to hook into the already-present dashboard monitor syste? Now you need to ensure that the camera and the dashboard hardware talk to each other reliably even though they are made by different companies. I've had a phone where the camera would occasionally stop working until a reboot.
The automaker is buying *millions* of the same camera. You've never heard of price breaks?
The company I work for sells expensive industrial equipment that costs our customer tons of money if it's malfunctioning due to a faulty component (and we are on the hook, too, if the yearly downtime hours exceed a certain threshold). The components that we buy from our suppliers need to comply with many pages of requirements and the suppliers need to provide a paper trail of all the quality checks and test results. Believe me, that does not make things cheaper. I suppose that the car industry is more price-conscious than we are, though.
You say: "it's cheaper because they buy them by the million". I say: "it's probably not cheaper because of (1) quality differences, (2) labor/logistics costs, and (3) need to have the same camera model on stock for 10 years." But neither of us really knows the numbers.