The 3rd party guy isn't paying someone $40/hour to install the $20 unit. The $20 unit will not be as integrated into the car and will have the look of an after market part. Does the $20 part only come on when the car is in reverse, or is it on all the time? There's a lot of reasons the after market thing can be $20 and a lot of reasons the auto manufacturer's is not. It's not all down to greed