Two years ago I bought the cheapest available (around GBP 90) meeting the following criteria:

  • Android version > 5.0 (this was 2 years ago, so likely you need to up that version)
  • MicroSD card slot. You’ll generate a lot of data, so you DONT want it fouling up phone storage
  • Good Battert life. My first smart phone just didnt have the battery oomph to handle running the GPS for more than about an hour. I think you want something in the order of 2800 mAh.
  • Memory needs to be a decent size, as does phone storage (all those Google apps take up acres of unnecessary space), but I don’t have a figure off the top of my head.

Obviously requires GPS & Camera(s).

Most of the OSM apps can me moved to the SD card, but updates tend to move them back to in-phone storage.

These will tend to pan out to one of the Chinese models, often badge labelled by, and tied to, a given network operator.

HTH