I think you'd do best forgetting the rear cam for now and get a better front cam, since almost everything you need to protect against while driving happens there. LA summer heat means you'll want a capacitor-powered cam; batteries won't last long there. You need a quality SD card which many cams do not include. If you can install a GPS, you can install a dashcam, they're essentially almost plug and play. Hardwiring can be trickier but we can walk you through that. Hiding wires is pretty simple, but the factory PS cable may not be long enough. That may mean getting a separate PS and longer cable. Parking mode doesn't work well with cheaper cams due to start-up delays of a few critical seconds, and pre-buffered cams will exceed your budget.
If you really must have a dual cam, the Blacksys is about your only decent budget oriented choice. It comes with a smaller SD card and everything needed to do the average install. It's pretty good but some have been reported to have died a year or two down the road. Same as anything else, you don't get what you don't pay for which is why I think you'll be better off putting your money into one better front cam. Later on you can do a rear cam, or upgrade the front cam and use the old cam in back.
Phil