I have recently bought a Veho Muvi K2 4K (cries of nay from the fashionistas and gotta have what Joe has next door) for the princely sum of £69.00 on eBay from cameracentreuk, performance is good, picture quality is excellent, bit fiddly to use, (especially with sausage fingers!) but compared to the price of a GoPro, I can live with it getting broken.
SD card storage max is 64GB so can be a bit limited if you are planning a long ride etc, but works fine for me, also all comes in a nice plastic storage box with multiple mounts, detachable screen etc.
Think the retailer is on Amazon as well, so bonus!