If you want a speed and time stamp then you'll likely need to buy secondhand as dash cams with this function are usually over £50. I think the best option for you would be the Nextbase 312G, it's the older model but very decent (including speed tracking) and it's about £52: amzn.to/3a52VzL

The upgraded Nextbase 322GW is about £95 but offers better features and resolution.