With that budget you should be able to get your hands on a machine with plenty of power. My recomendation would go to a lenovo t480/t480s. I was planning to buy one of those for myself but my current laptop is still good enough. Regardless of the device you choose, I would recomend portability over power: power efficient i5 4 cores, 8gb (idealy 16gb) ram, ssd storage, lightweight and good battery.
To answer your last question, you shouldn’t be concerned about performance. Linux can give life to old hardware, but you’re not really looking at old hardware.
As a cybersec student myself, I would suggest starting out with a generic linux distro and just install the tools you need as you go. If you really need kali, install it in a vm. I say this because I expect you’ll use Linux as your daily driver, and Kali is NOT mean to be a daily driver, but a tool for when you need it. And “when you need it” will come with experience I guess.