Here's a comment left by a friend of mine in New Jersey. It seems like she has found a more frugal way to ship things from the USA to Bolivia. Leave it to resourceful homeschool moms to find a better way! Thanks Sally for your help.
"You can order flat rate bubble wrap envelopes from the postal service. You cannot get these at the post office, only online. They are free and are shipped free. Do not ask me why you cannot get them at the post office! They can take up to 4 pounds of stuff and the rate from the USA to Bolivia is $13.95. This is the cheapest way that I have found to ship overseas. If you can fit it as they say you can ship it. I sell on Ebay and found this out through shipping so much. This is way cheaper than 4 pounds to Bolivia any other way."