Best type of "pulley" material

[Nitroxextreme]

My team has decided to use some sort of pulley/tread system to get the balls off the ground and into the hopper.

However, for the distance that we are going for there just are not any standard lengths. We have done some research into the endless belts, but have not found any easy way that we can make them ourselves and have them be strong.

What kind of rubber tube, flat belt, etc. would be easiest to make a custom length and where could this be purchased?