Sorry, but "cheap" is very relative, and it depends on the country or even the city you live in.
It's best to look up the Unity editor requirements:
https://docs.unity3d.com/6000.2/Documentation/Manual/system-requirements.html
With that, you can look for deals near you. Maybe second-hand stores if you're on a tight budget.
A powerful but older computer that isn't compatible with Windows 11 could be a good option if you install Ubuntu, for example.