There is an easy way to make them all at once:
Make a sandwich of styrene discs. If you rough cut the number you need, and bolt them together through their center holes (which I assume will be required), you can then finish them all at once with a file.
This way you only have to do it twice; once for the outer parts of the pulleys, and once for the inner parts.
Once you have finished both sizes, take the discs off the bolts and glue them together to make your pulleys.
Enjoy!
Bruce