How old is your son and how generally in to gaming on PC is he?
Are you ok with a desktop for this use instead of a laptop? You still get more perf/$ if you have the space to set up a desktop.
This one on sale at Newegg would take on basically any general use and gaming up to 1080P and I believe even meet the requirements for a VR headset.
https://www.newegg.com/Product/Produ...61&ignorebbr=1
Then add on a 23-24" 1920x1080 monitor for between $100-150, and a pair of headphones for <$25
Dell's Inspiron Gaming desktops look like pretty solid value for 1080P gaming desktops as well.
http://www.dell.com/en-us/shop/dell-...gaming-desktop
That would get you a solid gaming system that is also usable for basically any general purpose tasks.
If you'd like to spend <$500 all-in, I think you'll need to look at refurb units a generation or two old, but it should still be doable.