Future in the Air Force?

Hi, I'm a high school junior and I'm looking for an opportunity to join the U.S.A.F, I know that there's a AF ROTC program, I think this program is only available in certain school, I've heard people said that I have to pay for the Air Force for my benefits later which I don't really understand. I'm mean like if I join the ROTC, all I have to do is have my commitment and serve for certain years, and then the ROTC of the Army will pay for me to go school right? So how comes the A.F want me to pay, is this like some kind of tuition? or like an enlist fee? because I really want to serve, but by my knowledge not my money, and my family financial problem is very tough, so I don't think they will like the idea of paying for me to join. So if you guys know about this clearly, please explain for me! And if I don't use the AF ROTC, and just take regular classes in college and university, will I still have a change to become an A.F officer? I want to be in the Space command, so what kind of degrees that I need to work there? Thank you for your help!