GearBest offers the Excelvan Q8 4K WiFi Sports Action Camera in Black for $49.96. (Click on "US Plug" under "Custom options" to see this price.) Coupon code "gbq8c" cuts that to $39.99. (Doogeegrow via eBay has it in Silver for the same.) With free shipping (choose "Unregistered Air Mail" at checkout), that's the lowest total price we could find by $10, excluding other eBay vendors. Features include a 2" 320x240 color LCD, 170° wide-angle lens, up to 4K video recording at 30fps, 16-megapixel photo resolution, built-in microphone, WiFi, micro-HDMI, micro-USB, TF card slot, rechargeable Li-ion battery with up to 90 minutes of run-time per charge, waterproof housing, and multiple mounting options.
Note: This item ships from mainland China and will arrive in three to eight weeks.