The plans are all over the place.
Have a look at these threads.
Beyond that I’d do either a grandfather plan if you can find on ebay depending on data usage or Visible
Calyx roaming on t-mobile looks like a good option as well.
Ultra.me is another option, all plans make work for a period of time , then be discontinued by the plan provider, so be aware and have backup options.
For commerical services we sell data by the GB , which is expensive , but isn’t used heavily and works for our customers.