Reddit mentions of Lightdow LD6000 WiFi 1080P HD Sports Action Camera Kit - App Remote Control 30m Waterproof 2.0 Inch LCD Screen 170 Degree Wide Angle 2 Rechargeable Batteries and Mounting Accessories (Gold+WiFi)

I've used [Lightdow 6000] (https://www.amazon.com/Lightdow-LD6000-Sports-Action-Camera/dp/B00XC46TC4/) currently $39. for a couple non-quad projects (I actually have two of them)

It is cheap, has a crap ton of GoPro style mounts, and generally works pretty well. Low light performance sucks, there are only a few white balance option... the biggest problem is that there isn't a good way to remotely control the camera other than wifi

If you want to control the camera via your transmitter, don't go here... unless you want to do some hardware hacking.

It looks like there is a 4k version for a little cheaper.

I got one for free through ART USA. I think its pretty good but I never would have ordered one for ~$50 because I was expecting junk. The image and capabilities are impressive compared to a real gopro and its price.

[This looks identical to the one I got.] (https://www.amazon.com/dp/B00XC46TC4?psc=1)

Most of the offers suck but sometimes you get lucky.