If he’s over 6 foot, happy to buy 2nd hand and wants a do it all bike that’ll handle the uphills, downhills and everything in between, then he could do worse than look at my Turner Flux that I’m about to re-list for sale at below that price 😉
Otherwise it really depends on what he wants to do with it. In truth he’s not going to get much for that money, low spec etc. Best bet is to focus on getting a good frame/shock/fork combo and upgrading the rest as and when. The Giant Trance is possibly a good bet. Best of both world 27.5 wheels (Giant own-branded but believe thay are DT Swiss as with their road bikes), good frame for the money and more flexible in what it can handle.