Believe it or not, some high end vehicles like this Porsche Cayman GT4 did not come with the option for a back-up camera! In cases like this, we have a few options. A very integrated solution would be to go with a module from NAV-TV which is able to decode the factory head unit and add parking camera inputs, HDMI inputs, etc. Because these are car specific options, the research and development costs are quite high so the modules are typically $800-1000. That's before the cost of the camera and labour of removing the factory head unit and running the wire to the rear bumper area.
Alternatively, a universal screen and camera setup would be cheaper in terms of parts but offers a less factory fitted look since there is an external screen. External screens may be attached to the windshield, placed on the dash, or integrated into a rearview mirror unit. Some of these rearview mirror screen + backup cam combos actually offer video recording functions as well! In terms of a dedicated dash cam setup, they're typically not as good as offerings from Blackvue, Thinkware, or VIOFO but from a value standpoint, these combos are excellent.
Our customer went with this kind of setup which features a large screen that spans the whole width of the mirror. It has a nearly 10" wide screen and records 1296P front and 720P rear. Installation-wise for a car like this, the hardwiring of the front camera and routing the wires for the rear camera takes around 4-5 hours. Because the rear camera needs to be run to the outside of the vehicle, in some cases the bumper may need to be drilled. The rear camera is wired with a trigger so that the screen will automatically display the rear feed when the car is shifted into reverse. During normal driving, the screen will be off allowing for a clear view of the rearview mirror.