It looks like this:
https://www.amazon.co.uk/Iwata-Universal-Spray-Out-Pot/dp/B01DYN6ESG
(You don’t need that specific one though - they’re all the same).
Pick up a spray-out pot:
Eliminates overspray when cleaning out & between color changes, plus acts as a stand holder!
Make sure you buy a hose if you buy a compressor without one (eg. if you buy used).
You will want to buy a respirator.
You can also jump-start his accessories list by including some cleaning supplies (spray-out pot, airbrush cleaner), as well as some paints/primer/topcoat (tamiya, mr color, vallejo, alclad ii, etc.).
I believe this can all be done with a budget of 300$ (assuming US). At this point, he could start spraying that day if he wanted.
EDIT: I use this Master Airbrush Compressor and the Iwata HP-CS airbrush. I've been happy with them so far, but I do wish I spent a little more on a compressor with a tank (as /u/7x13 recommends).