if you can wait, Amazon Black Friday/Lightning deals before and after Xmas are as cheap as you’ll get in the UK. I’ve bought several for us and ‘for’ mates (as in I see the deal and snap it up, they pay for it!) in the last 2 years, everything from Etrex to Edge 500 and 800 to various multi-sport watches. We’ve paid less than I’ve seen them go for used.
If you miss a deal you can save it and they’ll notify you when it comes around again.
Other options are to keep on eye on Wiggle, CRC for “NOH” which means factory-refurbed, and discounters like Handtec or Sportpursuit.