Your looking for round braided or woven belts, like the ones on dental drills.
If your going to use belts, calculate what you torque and inertia requirements are, then size for the pulley's.
Your limiting factor or design consideration for the belts is FPM (Feet per minute).
An idea just popped in my head; what about sacrificing torque for inertia by adding mass to the spindle. Might take some time to come up to speed and PCB having such a short work cycle (time to drill one hole) that it might help lowering the FPM to a less expensive belt (larger drive pulley). Have to watch the spindle speed to make sure it didn't drop bellow limits, then pause until the spindle returns to speed.
Wrap that mass in Kevlar blanket!
High speed spindles can be deadly, the life you save could be your own!
