How far is the nearest Internet? Can you create an air bridge from there? If the companies won;t run the backbone, that could be an alternative. You'd need a high spot on either end but you can go 20-30 miles between points. The best part is once you do that you can offer Internet service to everyone around the school.
How abut cellular service? I think AT&T & Verizon have rural Internet service packages. It's more limited, but would give you Internet access. Even if the cellular signal is weak, you can use external antenna's to improve the signal.