I've finished a bellows as well a few days ago, for a 4x5" enlarger I'm building, and which is almost finished. I also found it very exciting and actually easy to fold it and see it come to life progressively!
I'm rather astounded by the price of your bellows ($60). Mine have costed 4 euros. That was the price of 45x100 cm of black and thick adhesive, the one you find in the wallpaper section of shops. The rest was just some cardboard and a matte black aerosol painting for the inside.
The size of the bellows : 16x13cm, and it extends from 6 to 35 cm.
I've followed an old article I've found on the web :