UK is a bit more expensive than that but not silly.

I can get close to £10/mo but that's because I'm already paying that carrier ~£30/mo for two separate SIMs (mine and my kid's).

The £9/mo deal offered below is just half price for 6 months, it then becomes £18/mo.

https://5g.co.uk/unlimited-data-sim/

The bottom of the page does give some details about what "unlimited data" means here in the UK between the different carriers. Some cap speeds, some monitor usage and then either turf you off on "fair use" grounds or do traffic management/shaping. The general rule seems to be 650GB in 6 months is just about the limit of what is ok.

That wouldn't be anywhere near enough for me. Looking at my router I see I've downloaded 522GB in the last 34 days alone.