The use case I'm trying to solve for is an urban location where sensors are sending MQTT data on an occasional basis and not using more than 1 or 2 GB per month. At the moment, the Google fi SIM is the most cost effective, but it isn't scalable in a business context.
What are others doing to resolve cellular data connectivity at a reasonable price?
If you are just prototyping and not ready to create a relationship then use one of the online plans with a provider or Twilio etc until you are ready. You'll generally pay a bit more doing this, but for prototyping it gives you more options and you can try different providers etc.
They have many data plans and have worldwide support.
But their SIM is embedded in SoC.