In reply to Fishmate:
To give you an idea of what can be bought, I recently got one of these for £15.69:
https://www.amazon.co.uk/dp/B071H7SNLJ/
I stuck in a GiffGaff SIM, sent it the setup commands, and it talks very happily to my Traccar server. It communicates via GPRS, and is using bugger all data, at 5 minute update rates.
It's not waterproof, and has no collar mount, but I have seen such things for not much more. Check that devices really do have GPS; there are a lot of cheap trackers out there with GPS in the name, or on the device, but they are only GSM, giving details of the base station.
I can use the Traccar Manager app to track devices on my smartphone.
Traccar is free and open source. The server runs on a small windows PC, or you could just use the demo server.
Post edited at 03:46