I didn't care if it looked original or not--it's not like I'm restoring a classic car--so I decided to use craft felt instead of automotive fabric to save money. To save time, I decided to stitch the felt around the edges with a blanket stitch instead of trying to reverse-engineer the original construction.
The materials cost me just over $2, and the project took about 3 hours including buying materials.
Even if your sunvisors aren't falling apart, you could use this method to add some color or even customize your sunvisors with appliques or glued-on felt designs or letters.
I made this at TechShop San Jose (www.techshop.ws).
Step 1: Purchase materials and gather supplies
72" wide craft felt (Measure the depth of your sunvisor, double that amount, and round up a few inches; mine took 1/2 yard) (1/2 x $4.99/yd)
1-2 packets coordinating embroidery floss (mine used slightly less than 1 packet, but your sunvisors may be larger or your stitches closer together) ($0.39 each)
Pen (for marking fabric)
A few pins
Screwdriver (to remove/replace sunvisors; check your car, mine needed a Phillips head)