for around £100 there’s this
It may need a little assembly but everything you need to get airborne is in the box.
BUT before you do that, first find your local flying club. Go watch them fly. Ask some silly questions, and some not-so-silly questions. Find out if anybody is willing to train your son. Then find out whether they fly Mode 1 or Mode 2, and what would they recommend. They’ll probably recommend an IC model but stick to your guns if you prefer electric flight; it’s gaining ground all the time on the smelly noisy infernal combustion engine
Eventually you might come back to this model, or you might not, but at least you’ll be doing it with some sound advice rather than a bunch of mountain bikers on an internet forum 😉
You should also check out BMFA, if nothing else they’ll be able to show you where your nearest clubs are.