A handy thing for this situation is a second hand machine. It is a whole lot cheaper, still very much an upgrade, but reselling for a reasonable price is possible.
The option I would actually recommend is to reinstall your OS. A fresh install if Windows or Linux is like a new computer in many ways. Add a few changes, like maybe changing theme and trying new software, can also make it better.
If you wanted to satisfy that ADHD itch with Linux I would recommend trying something like ElementaryOS if you come from Mac world or EndeavourOS with KDE if you are from Windows world. Great operating systems with sane defaults and an easy install but well put together appearance and utility.
Also, if you know where you are going maybe consider researching local options from there? Like calculate the postage, find the local stores, look for local second hand computer stores, etc.