I explored a number of options with this a few months ago, asking a lot of friends, social media connections and if I recall, asking here too.
My goal was to be able to document traffic incidents or collisions and such while driving. I was also pondering interior views for potential criminal activity.
My concerns were it needed to be wireless (keeping installation simple and saving video for the "what if" moment needed to be automatic), in that I could recall video of an incident. It needed to be on the smaller side, capable of being mounted to, or around my rearview mirror and "camouflaged" to blend in with the windshield. The Onstar and lane sensor/collision avoidance console behind the rearview mirror gives some nice cover to blend in. I wanted HD or as close as possible and video stored to an SD card which would write/re-write over itself if nothing was going on. Essentially, I wanted it to be hassle-free, or as close to it as possible, almost "fire and forget", so to speak.
Lastly, it needed to be reliable. I had looked at many, narrowing it down to two; Either Cobra, or BlackVue (of course I can't find the website now as it was several months ago, and I've since replaced the laptop I'd saved all the info for it on (backing all your info up, only works if you are consistent and I'm not.
I remember leaning towards the "BlackVue" packages, they sell combo (both front and rear) which I didn't need and wanted a forward facing camera with as wide a field of view as possible. Recording the interior, or dual camera wasn't a priority, but several offered that option as well, with motion detection that would turn the camera on when someone broke into the vehicle. I'm not sure if you're looking for a 360 degree camera to use with parking assist and such, but if you are, their options might suit your needs. Cost of these is like any other electronics these days, ranging from 500+ to 29.95 for stuff made in China and sold on Amazon or Ebay. I'd suggest a quality camera, Uniden, Sony, Garmin, even GoPro is getting into the market for it. I was concerned about having a camera stuck to the dash and "inviting" someone to break into the car, thinking there was a payday to be had.
I didn't follow through and I should, being able to document things and having video of a collision can be very helpful when it comes to dealing with insurance, provided the collision isn't your fault, of course.. ha ha.