Not sure what the availability is like at your age, but maybe join some skills camps? A nutritionist and trainer both sound like good ideas. I think paying a person is a waste of money if you can afford a ball return net(Amazon link: https://www.amazon.com/iC3-by-Airborne-Athletics-Basketball/dp/B00AXM2PJO). This way you can shoot around whenever you have spare time, instead of relying on the schedule of someone else. I wouldn't go crazy with the skill accessories if I were you tbh, just get shots up in your free time and practice whenever you can.
Shooting machines like The Gun or Dr. Dish are sizable investments. I don't know what your definition of expensive is, but if you go on their sites, they ask you to call for pricing, and that's a good indicator of how expensive this stuff can get. A similar machine on Amazon was priced at 5000 dollars, and I don't know how much cheaper it can get from there.
You can get something like this for about 600 dollars. Or one of those "ball catch" attachments for a basket will only be about 50 bucks.
I think just making a friend will be so much cheaper, more effective, and in the long run, more fulfilling than any of those options, though.