I bought one of these from Stapleshttp://www.staples.co.uk/youngstar-black...CFYvpwgodZ38AgA
£40 in the CURRENT Staples Sale
Simple very wide angle camera with a fully waterproof plastic case. IS waterproof - I took it snorkeling on holiday in January and no problems.
Very wide angle gives a bit of distortion in normal use (minor) but that cancels out when it is used under water.
Takes a micro SD card of whatever size you want. I have a 16GB which will give me a couple of hours video which is also about the battery charge life
Battery recharge is micro usb
Camera stays in the waterproof housing even if used on a car dash because there is no mount screw on the camera (too small) only on the case. Drawback of that is you cannot keep the battery charged as you drive because no (easy) access to the usb charge socket
Kit comes with a mount that will put the case + camera on the dash (or a bike helmet etc) and you can get universal handlebar adaptors easy off ebay.
Pic quality is perfectly good enough and at night is sensitive enough for normally lit roads.
Worth thinking about for under £50