Plans vary between countries, but in Australia at least they have a 5GB for $15 AUD (~$10 USD) backup plan. You can also pause it when you don't plan to use it

Plans vary between countries, but in Australia at least they have a 5GB for $15 AUD (~$10 USD) backup plan. You can also pause it when you don't plan to use it, so then you effectively do PAYG, activating it only as required.