I've had my eye on doing a setup like this, haven't pulled the trigger yet. They have a bunch of great mobile DVR units on Alibaba, including 4, 6, and 8-channel models (search for things like "bus dvr"). Thinking big for camera locations for an all-out system:
1. Front windshield
2. Back windshield
3. Left side
4. Right side
5. Rear bumper
6. Front bumper
7. Driver's side rear bumper
8. Passenger's side rear bumper
9. Driver's side front bumper
10. Passenger's side front bumper
11. Driver's side mirror (blindspot)
12. Passenger's side mirror (blindspot)
Those cameras in useful combinations:
1. 360-degree crash-cam DVR:
This records all angles of your car for accident footage.
a. Front windshield
b. Rear windshield
c. Left side
d. Right side
2. Blindspot cameras:
This is for merging or changing lanes. Honda has it setup to activate the camera onscreen via your blinker.
a. Driver's side blindspot
b. Passenger's side blindspot
3. Backing out:
The problem is getting a full 180-degree view when backing out. I have a little car, so if I'm sandwiched between two giant SUV's, rear visibility is useless because I can't see what's coming on either side. By doing a split-view on the screen, you would get a half-circle of coverage, so as soon as you started to back out, you'd see exactly who was coming on either side of you. Just wire in the onscreen camera activation to a taillight, so it turns on automatically when you go in reverse.
a. Rear bumper
b. Driver's side rear bumper
c. Passenger's side ear bumper
4. Parking in tight spaces:
Landrover has a nice setup for this - it gives you an angled view of the street, including on the front bumpers, which makes parallel parking a breeze if the spot is tight or you're having trouble with depth perception.
a. Front bumper (how close you can get)
b. Passenger's side bumper (parking close to a curb)
c. Driver's side bumper (parking close to another vehicle or other obstacle)
Pricing really isn't bad at all, at least compared to the competition like BlackVue. A quad LCD is only $85: (setup a simple switch for backup mode, blindspot mode, parking mode, etc.)
http://www.amazon.com/TFT-LCD-Rearvi...dp/B00F36ZCGI/
Most cameras only run about $20, so even if you buy 12 of them, you're only out $240:
Swivel camera
Flush camera
Under mirror camera
There's a zillion options for mobile DVR's as well...record to shockproof SD cards, add GPS location, remote viewing via 3G, timelapse in parking mode, extended recording to 2TB 2.5" drives, etc. You could pair up a standalone 4-channel crash DVR for $180 and use an 8-channel mobile DVR for switching the viewing modes. Here's one for $370 on eBay:
http://www.ebay.com/itm/8-CH-Channe...-Recorder-DVR-Camera-System-GPS-/171293720973
That's going to the extreme tho ($900), but I think it would be pretty cool because you'd get full coverage for accidents, as well as tons of added safety & convenience features (full-view backup camera instead of just a wide-angle lens, blindspot cameras, etc.).