High value-to-weight shipping

I was doing my econ history class tonight, and we were talking about the changes in ocean-going shipping in the early 19th century, in particular that one big item being carried was mail.  I pointed out that mail was a highly valuable thing to ship at the time, because it was about the only way to get information from the US to Europe and back.  And I sort of off-the-cuff asked how much the USPS charges to ship a ton of first class mail today.
 
$14,720.
 
32,000 ounces in a ton, times $0.46 per ounce...
 
I guess mail is still a high value-to-weight thing to ship...