There are lots of great deals in the January sales, and towards the affordable end of the scale is the Garmin Forerunner 235 reduced to just over £159 on Amazon
The Garmin Forerunner is a fully-featured sports watch, offering Garmin's Elevate wrist-based heart rate tracking and GPS. It normally retails for around £175 (the RRP is £299.99).
Garmin Forerunner devices are aimed at sports first: they are class leading for runners, with GPS and motion detectors to give a complete picture of your workout.
Waterproof, compatible with training plans, it will also give you advanced fitness metrics like VO2 Max to keep your training heading in the right direction, while offering a customisable workout display so you can see the information you need easily.
The Forerunner 235 connects to your smartphone (Android or iPhone) via Garmin Connect, bringing over notifications like a smartwatch - but with a battery that lasts much longer.