The wireless suggestion is your best bet. You basically have two choices here. Frequency hopping or fixed. Use can use a directional antenna or an omni. All of material can be bought new or try e-bay. This is unlicensed spectrum and with the right equipment both voice and data can be sent. Of course you could run fiber. Since you are an educational institution, I,m sure it would not be difficult to get a right-of-way agreement. Hire a contractor and have some fun!