I know a lot of teams had great success with Orangle Eagle 85 belts from Fenner Drives (
http://www.fennerdrives.com/) you can order them from Mcmaster. Most teams I've seen use it with what amount to a customized soldering iron to fuse the belt together, thought fenner's website should give you more information.
Belt Diameter Per Foot
1/8" 59725K702 $0.45
3/16" 59725K703 0.65
1/4" 59725K704 0.81
5/16" 59725K705 1.26
3/8" 59725K706 1.76
1/2" 59725K707 2.96