My Boyo from Amazon has a great picture. I mounted the license plate type up high so it looks kind of unusual above the rear doors, but the picture quality is great played through my Pioneer head unit.
Camera was about $65 and Pioneer DVD head unit was about $250 I think.
I can provide part numbers if you'd like. My head unit came from Crutchfield.
Is your monitor or camera an Audiovox, or both?
I don't think I'm going to get much better quality with a coaxial setup, which most of these are.