Just to reinforce what all the thread is saying: used Thinkpad in ebay. I would search for a x270/x280/t470/t480. This depends in screen size.
Why these models? They are the last ones that allow you ti upgrade your RAM, so when you have a bit more money you can upgrade. Also, these are old but not ancient, so they can still be relevant for some time.
On the other hand, if you have more budget, the best Linux laptops are the frame.work, but they're expensive, although they're reparable and upgradable, so I guess that depends on how you see it.
Finally, Kali is not a daily use distro. If you have time to waste (or invest) then you can go hardcore and straight to Arch Linux. If you want to have an easier journey you can start with PopOs!
Good luck on your journey!!