Not many 2-channel cams worth having out there for $125. None will have good vid quality on the rear cam, and just a few are good up front. Parking modes other than low-bitrate recording and time-lapse are generally not any good in cheaper cams, and that will require a hardwire kit at additional cost. You'll also need a microSD card too, and not just any will do but they're pretty cheap right now.
That price can get you a good single-channel cam, but you need more budget to add a rear cam.
Phil