In reply to Euan Todd:
As per the posts above.
Barometric altimeter and proper mapping may well take you over the £200 point.
I have the Garmin Forerunner 245. 24 hours battery in GPS mode and allegedly longer in ''ultratrac" mode, which turns the sample rate down, but gives a cruder representation of the route followed when you input it into Strava etc.
It does give GPS based elevation, which was surprisingly accurate when I measured it at known spot heights (+- a few metres).
Navigation is very basic. It has options to return to the start by either following the track back or direct line. You can import waypoints manually but it's too much of a faff forr me to bother with.
TBH if you set it up to display 6 fig OS Grid and GPS elevation info its easy enough to find yourself on a map if you get lost.
I've found the wrist HR quite useful, and the Garmin metics like "body battery" and "training status" which I thought were gimmicks actually seem to have spotted I was going down with flu a few days before I had symptoms.
I'd be wary of second hand watches. Check the battery carefully, because once that starts to fail the watch won't last much longer.