I've shipped over 200 lenses using USPS, domestically and to about a dozen countries, with no trouble. I usually do something like this:
- put the lens in a plastic bag to keep dust and styrofoam bits out of it
- bubble wrap
- foam packing peanuts around that
I don't like to use those balloon things that Amazon uses. I imagine them getting punctured and suddenly not providing any protection. Newspaper works in a pinch.
The post office will give you a medium flat-rate box, which has way more room than you need for the lens and packing material. You might pay a buck less for shipping if you have a box and pay by weight. I print labels online so I can get electronic delivery confirmation for free and a slightly cheaper price.