This is like a hipster PDA, but better!. It is more durable, sturdy, and easier to replace cards.
As many index cards as you want pages.
Two pieces cardboard, thin enough to cut easily (see step 2 for information on the sizes you are going to need to cut it to)
3 Binder Rings (available from Staples in a pack, may be called "Book Rings")
Step 1: Punch Holes in Index Cards
Choose how many index cards you want, and using either a one-hole puncher or an adjustable 3-hole punch with holes 2 and 3 removed (that's what I used) punch a little at a time to have the holes look like the picture.
The first time, punch the holes. The second time, use one card from the first time as a reference, so the holes will line up.