Hi Logan
You probably have already, but if not, you first need to work out the design of the machine. Plenty of on-line designs out there. What motor, gearbox, reduction box to achieve the speeds you want determines what pulley diameters you will need.
"V" belt drives seem to be the way to go and probably cheaper than Timing Belt systems and will give a positive enough drive, with the correct tension on the belt
http://www.artinso.com/astronomy/mir...ngmachine.com/
A few examples in case you hadn't seen them yet. As you are on Cloudy Nights , you know that they are an excellent resource for links an help as well.
Have Fun
Jeff