Most places have no problem, some even will transport it for you free of charge when they here its for a good cause. At the bottom of the tank you can put small tiles which have numbers on them. Each jumper is allowed to bring up as many tiles as possible. At the end of the night, major prizes are given out according to the numbered tiles. Get your directors involved by seeing how much money the crowd would give to get them to dive in, too.
Many schools run a festival or band day for high school students.
Money comes from registration of the high school members, t-shirts, or help from the college program. Ask your music department first if they will be willing to help with the festival because it is a great way to recruit future band members. Your chapter can organize and charge money for tickets to such an event for your band program. Themes are always a good idea.