[richardhawthorn]

1nce [0] and Hologram [1] offer low cost SIM cards for these type of applications.

1nce for example charges €10 for 500MB of data which lasts 10 years. Assuming you are economical with the data it's €1 a year, which is a very appealing price point. Even if you need 500MB a year that's still less than €1 a month.

Hologram charge by the MB (although I'm not sure exactly how much as their pricing page isn't fully transparent), with a 70¢ a month charge per SIM card. I think they offer a free SIM card with a certain amount of data a month free (maybe 1MB) if you just want 1 SIM card.

[0] https://1nce.com/ [1] https://www.hologram.io/