Are you planning on going to college? Do you have any plans for when you graduate? Or are you going to start working right away? My advice to you is if you're not planning on college would be to lease him out and maybe join the military? Air force is pretty good. Lease him out for at least a year to get your training done, then you can bring him wherever you are. I know that the stables here on post are really nice and are not at all expensive. Plus the military will pay for your college too and it will allow you to get alot of good experience.
But if military is a nono then you have 3 options; option 1, keep your boy and take the bus everywhere. Option 2 is sell him, or option 3 is lease him out until you get on your feet. Starting out is hard when you're doing it on your own. I moved out of my parents house 6 days after graduation. I didn't have a horse or anything, just a cat and a dog. But I had to take the bus everywhere until I saved up enough for my first truck. My first truck was an 89 ford that had major body damage, I bought it for $600. If you save up to buy a car straight out then the main thing you'll have to worry about is insurance every month. I'm 24 now and have a honda civic 2 door, insurance is $90 a month for it. Do you know where you'll be living yet? Because you have to figure in rent, utilities, and food too. It's scary moving out on your own but when you look back and realize that you made it through some hard times you'll feel so proud of yourself. If you do keep him and not lease him out ask the BO if maybe you can work at the barn once a week to take off some of the price? That's what I do. Saturday evenings, 2 hours. $80 a month. Or maybe ask if you can work a couple days a week for the feed and do a lease like thing with them? So anytime they want to use him they can?
It's a shame that these days we can't ride out horses everywhere anymore, I'd prefer that to cars any day. Except for long road trips, I get bored on those.