My issue with cheap dash cams is much the same as with any tech: it's a false economy in the long run. You can get plenty of cheap options online but they won't last long and many of the ones I've tested don't work properly - i.e., they stop filming, files get corrupted etc. These cameras don't often come with any warranty or customer service if anything goes wrong either. But if you can find a cheap one on Amazon with decent reviews, there's no harm in trying one.

My suggestion would be to get this £80 Apeman option (and a Micro SD card as it won't come with one): amzn.to/2E9RRXI