I`ve used one of those cheap Bullet camera`s from e-bay (£25) shocked that the battery life was around 4-4 and half hours, records in 1080 or 720 and video is in increments of 3 minutes, had it for 2 years still performs well, however the sound quality is atrocious when moving.
Yep, this has been the case with all cheap cameras I've had. Vibrations from the bike are heard, or even amplified inside waterproof mounts, because it is difficult to check before buying.
I'm currently using an "Action Sport" from The Range. It was something like £25 because I won't spend so much that I get upset if I kill it: it's been dropped in a taxi, left outside in a hotel garden, come close to falling off the bike into a Flemish canal, ... It has a screen (which switches off after a couple of minutes) so it is easier to aim than my old bullet camera and easier to check and set the time/date (which is required to be correctish if you want to use it in a police report). It takes SJ4000 rectangular batteries which it is possible but a bit fiddly to swap because the battery door just bends to clip in, which won't last forever.
The most important thing is the mount IMO. A good bike mount will need damping in it somewhere. The camera came with a couple of converters to screw mount as well as a hard handlebar mount, but that transmits too much vibration. I got a cheap ball mount off the internet and the rubber grabbing the ball seems to work well enough to damp out most buzz (not perfect, but many of our roads are buzzy and bouncy as hell so I think you'd need top-end image stabilisation to cope). I've also got one of those bendy "gorilla" tripods which is also good bent through 90° as a mini selfie stick if you want to look around while on the bike, do arty over-the-shoulder shots. And I've a spring-loaded smartphone cradle from a discount shop so I can put the phone on the tripod for video calls, or for recording riding pieces with sound (not done that for any posted videos yet).
I've yet to find a good camera chest mount — those I've tried all suffer significant "droop" and leave the camera seeing far too much floor, which you don't realise until after the ride because you can't check the screen while it's against your chest. Maybe if I had moobs...
