This isn’t a cheap sport. His biggest stumble will be getting the cash for his initial certification. IF hes a mature kid, have him pay with a credit card and take some time to pay it off. (This was how I afforded LUXURY items as a kid. Id put it on a credit card and had a plan to pay it off in 6 months to a year. EVEN if I lost my job. There was always a plan to pay off my debt. )
After that, he can borrow and rent gear. Thats cheap enough.
Sadly, this is one of those hobbies that doesn’t lend itself well to ’budget’ operations. Make sure he’s REALLY into this before he starts spending money.