It's 60 cents for a single page letter in a #10 
envelope with an IPMO inside.  If you want to add 
another page to your letter, postage is a dollar.
If you want to mail via Global Priority, then it's 
$5 for whatever you can fit in the half size 
(5"x7") Global Priority envelope. It's $9 for the 
full size one (8"x10").  I've also seen Global 
priority boxes; they are about 2/3's the size of 
the shirt-size Priority mail boxes.  One of those 
with packing material and a cel in it will cost 
about $13-$15 to mail.  A box the same size sent 
regular air mail is about $7.

Hope this helps.

The Evil Jew