Bestbuy offers Nextbase Rear Window Camera for $30 (reg $100). Free shipping on orders over $35. 

Product Description:
Capture what's going on behind your vehicle with this Nextbase rear window camera. The 140-degree ultrawide viewing angle enables recording of details within a large area of coverage, and the fully adjustable magnetic mount provides flexible placement. This discreet Nextbase rear window camera works with a compatible dash cam via the included connection cable.

• Compatible with Nextbase 322GW, 422GW, 522GW, and 622GW dash cameras
  For use with your existing device.
• Dash camera attachment
  The camera can be connected to your main front-facing Nextbase dash camera.
• Rear window camera module
  Offers all-round protection to guard against everything, from tailgaters and rear-end impacts to knocks and bumps in a parking lot.
• Flexible recording options
  When you are using a rearview camera module, the resolution of your front-facing camera will automatically adjust to manage two high-resolution video files.
• 140° viewing angle
  Captures the whole road behind, including the road shoulder on both sides.