That post office worker must be out of his/her 
mind.  Express Mail for a small document envelope 
cost at most 17-20 dollars to Japan.  Air Mail= 80 
Cents and Registered Air Mail = $7.25  .80 = 8.05. 
All those methods take less than 5 days to get to 
Japan.  Never tried Global Priority tho...maybe I 
try that next :)

Express Mail is probably the best, since its the 
fastest and is treated as registered mail, its 
trackable on the internet and very safe, but its 
the most expensive.