Why not share the internet connection with everyone. 100 minutes for 600 people is alot. Setup an intranet or even a wireless network. Combine the minutes and you will have close to 42 days of internet access for everyone. ((100 minutes * 600 people) / 60 minutes) / 24 hours = 41.666 days.
If you limit the internet conection to evenings, lets say to 12 hours, then you can double that to 83 days.