That will cost you considerably more than the £30 a year I pay.
Not that I have noticed. I do connect to a 5G wifi signal from my 1Gb/s 3BB router via an Xaomei repeater, and use a good USB cable and power supply.
It will run on a hotspot from my phone if 3BB goes down, but not of course, if there is a power cut.
Anyone considering a Fire TV stick, make sure it is a 4K MAX, with operating system 7, as you cannot add extra USB storage, keyboard or LAN network connection to a 4K with OS 6, as I found out.