I'd look for a Pixel A series. They can be had brand new for a few hundred at Best Buy, or you could go the used route on Swappa to save some money. As mentioned above, old OS/security patches are a concern on the cheapest phones but Pixels have a few years of promised support from Google. They also tend to have almost all bands enabled for max network connectivity.

sky have some good international sim packages. I used one recently and it was really cheap