The UK ETA process is 'interesting'.
It costs 20 GBP per person.
They really, really want you to use their app. Available in English only 🙄 in the Google & Apple stores off course. Digital sovereignty anyone?
You can apply online, but it will take some stamina, e.g. clicking through the 'warnings' & 'helpful' messages before you'll land on a webpage.
Compare this to the free entry into EU for UK folks:
https://www.gov.uk/guidance/eu-entryexit-system
Borders are annoying.