Yeah I've heard the same for wireless systems.
You could also put together your own system. You really just have to pick out an lcd screen that can mount somewhere, and then a camera. Sonic electronix has a pretty good selection of backup cameras.
There's also rear view mirrors with built in screens, but I would only use one of those as a last resort. The video displays aren't very large, and when I tried one it actually obstructed my vision a little bit as well. While backing up, I found myself missing that part of the mirror where the video feed sits, since the video screen wasn't large enough to compensate.
It has been awhile since I wired a system up, but I remember it being fairly easy. Hook up the video screen to a switched power source, and ground it. Mount the camera, tap into your reverse lights for the power, ground the camera, run the video cable up the car to the video monitor, and you're done.
Do you currently have anything for a monitor? If not, what do you plan to use? I like this camera -- as it was hidden, and looks somewhat OE. The ones that attach to the outside of the rear plate stick out like a sore thumb.
Here's a pic of it on my previous ride. I may get it for my new one as well.
This, a $100 mirror, and 2 hrs of your time will get you decent setup. I wouldn't want a stand-alone monitor hanging somewhere.