For under $300, I would go for a used Thinkpad. I got a T460s for a few hundred bucks that runs linux wonderfully (jesus was the pre-installed Windows slow though). Linux usually runs much better than Windows on old low-end hardware. That 2015 MacBook has an Intel processor, so I would try Linux on that first as it might be more powerful than what you can afford to buy.
Kali is not an OS you would want to use for your main desktop, if you need those security tools you can run them in a virtual machine / live usb. I see you’ve tried to base your distro choice off of what you intend to do in school, which I think is a mistake. Choose your distro based off of the merits of the distro itself, as once you get past the package manager and release cycle, you can get the same experience on any distribution.
Before choosing a distro I would make sure you know the answer to these questions (in terms of what you want):
Stable or rolling release model?
Package manager (apt, dnf, pacman, zypper, etc.)
and these about your desktop environment:
What desktop environment (or standalone window manager) do you want to use?
Do I want to use Wayland or X11 as a display server? Does it matter to me which I use?
Does your distro have a spin preinstalled with your desktop environment of choice?
^ Also, if you are unsure about what some of this means, feel free to ask.