Windows PC upgrade

I keep getting messages from Microsoft on my Windows 10 PC, telling me to upgrade to Windows 11 before updates become obsolete. I'm fine with this, as my tower PC is rather old, having bought it nearly 9 years ago, in 2016, but anything with the same or similar specifications (below) now seems to cost thousands of pounds, rather than the few hundreds (just over £400, I think) that I paid. What's the way around this please? Should I buy a cheap laptop and upgrade the RAM and possibly graphics card and plug in my monitor and a larger 2gb external hard drive, with my files on, into it? Or are there any reliable cheaper tower options, with the same or higher spec please?