Before laying out any money I would check whether you really need a camera.
We bought a 2004 Autoquest 100 in June 2006 and found that all we needed was a Fresnel lens on the rear window which allowed a decent view through the central internal rear view mirror.
OK, it's a bit different to a car but, together with the large door mirrors, we soon became used to both reversing and checking the rear during normal driving.
Graham