I met up with @explorer the other day and he had a very cool onboard video system that he got off AliExpress or Wish, he couldn’t remember which,
I had a trawl on Aliexpress today and found a couple of units for just over $30US
This on is pretty good with 1080p cameras front and rear but the main unit doesn’t seem to be waterproof.
https://www.aliexpress.com/item/Motorcycle-Front-Back-Dual-Camera-DVR-Motor-Dash-Cam-with-Specialized-Dual-track-Front-Rear-Recorder/32885203044.html
Another one, not sure if this is waterproof.
https://www.aliexpress.com/item/KY-MT18-Motorcycle-Camera-DVR-Motor-Dash-Cam-with-Special-Dual-Track-Front-Rear-Recorder-Motorbike/32947311323.html
The prices go up from there to as much as you want to spend.
This companies products are getting good reviews on some UK motorcycle sites I frequent – Innov.com.
They are a bit more expensive than the Alibaba ones but have quite a few more features like fully waterproof connections and can also do GPS tracking via the supplied app on your phone.