Rather than a production bow for that price, I'd watch the classified section here for a quality used bow.
Also, his height has less to do with the length of the bow than does his draw length.
My first recommendation would be to have him read the Howard Hill bug thread here. It will take him several days, but he will be much wiser in terms of longbow does and don'ts. Lots and lots of great advice there.
It will also give both him and you insight into the types of "longbows" available: D shaped, Hill style, flat bows, reflex/deflex longbows, string follow longbows, and hybrids. Each has its own characteristics, pluses and minuses. It would be wise to have him make an informed decision. Then he will be more likely to stay with the longbow and traditional archery.