I started out using the camera (ActiveOn CX HD Camera). I dont know if I'd still recommend it, at the time I had paid $50 USD and it came with 2 action camera mounts and a waterproof case. Nowadays I'd recommend finding something that can handle 1080p at 30fps and 720p at 60fps. Reason being that they're not going to be overly expensive, audio is worth investing more into. If you're just starting out you can get by using a phone with a voice record app along with a cheap microphone, just make sure you wrap it in some deadcat to buffer out some of the wind noise.
I agree with others, I run a Hero 4 Silver and recently nabbed a second one - used once with all official gopro accessories still sealed for £62! My best advise is to keep an eye on Ebay and you will get a bargain if you look hard enough.
In addition to this, there are countless other 'budget' cameras out there which are very cheap and some are surprisingly good. I'm going to be uploading a comparison video shortly comparing the Hero 4 Silver to a budget camera I got over the holidays to see if you really can rely on cheaper equipment.
For sound I dont think you can simply 'cheap out'.. the gopro mic adapters are extortionate to be frank, and an external recorder would probably set you back just as much. Albeit being more useful as you can use an external recorder in other applications. My best advice here is to get entry level equipment like an adapter which may be expensive but will be vital in producing good quality videos.
Gopro Hero 4 does seem to be an old favourite. From experience I have went down the route of buying cheap, and honestly it ain't worth it. A lot of the knock off brands advertise 1080p etc but its all crap.
That being said buy what you can comfortably afford.
We have a few hidden forums and features that you can't see until you login or sign up. We only send about 4 emails a year and never sell anything. We're a global community for bikers who like to record videos. We run this site for fun