Ok, the first advise I have is slow down. Paintball is an edge sport, with a bad/misleading appearance and reputation to non-paintball people. So unless you know some one in the higher-ups of faculty that has extensive paintball knowledge you have to be careful. There is a stereotype that paintball players are dangerous, violent, wanna be army adrenaline ruled guys(or girls). While it is true that paintball is high adrenaline the others are not true 100% of the time. Another thing that you might take into consideration is is your son's school private or public. You will almost always have a much harder time with public than private. Reasons being, public schools have a much harder time throwing away money on a fringe sport like paintball(in my experience). Depending on where you are there can also be more violence in public schools(not always, but where I live), which could take away from your future paintball team. Next, how many kids do you have behind this movement. If you have only a few then your chances are decreased, not erased, but lowered. When I went to my principle to start about talking a club i pitched my idea, "and by the way, about an 1/8 of the student body said they might be interested in joining." Size of the want improves your chances. Next topic, don't ask for full funding right away. Unless you go to an uber rich school, when you tell them the potential cost, they will tell you were the door is. Start small, if you are looking for a free ride, from any source, for a brand new team you should rethink your strategy. Ask the school to get you jerseys with the schools logo on them, next year ask them to cover entry, next year ask them to buy one box of paint per event, so on and so forth. If you want instantaneous results, well, you can't always get what cha want.
This is all from personal experience. Every school will be different. Just because I said something definitely does not mean its true, i could be dead wrong. I am currently working on something that I hope will significantly grow high school paintball, so I can see what your going through. Feel free to pm me anytime if you have any questions.
p.s. sorry about grammar