Canon has a Virtual Lens Plant in which you can see how lenses are manufactured.
It’s a fascinating documentary video, and worth watching if you have any interest in camera equipment.
There’s a long process involved in just making even one piece of glass. When you consider that many lenses contain between 10-18 pieces of glass with various coatings, and with precision being of the utmost importance… you can certainly begin to understand why good camera lenses are so expensive.
You can find more geeky camera goodness in the Canon Camera Museum.