More than most in the UK. I pay £45/month with https://www.aa.net.uk/ for a more professional service than you'd get with the big providers. Comes with a /29, a /48, the ability to get real-time tech support from actual techies via IRC. I work from home so need a reliable connection.
Three's own MVNO (Smarty) gives you unlimited for £18 without long term contracts. It's £16 if you get it via uSwitch.
The problem with Three's network is that their 4G can be really bad in some areas (eg: parts London). I can't use them inside my flat because it's almost unusable during peak hours. On the other hand, if their 5G is available, speeds can be really good. It's common for me to get 100-900Mbps when near one of their cell towers.
I guess the point is for the average person an unlimited data sim is cheaper than a landline, let alone a landline and a limited data sim, so what's the point in a landline connection
Between line rental and dsl costs you'd struggle to get it that cheap through a landline, even ignoring the fact you still need mobile data.