As for the adhesive question, some of those envelopes do not seal, even if it has only 1 sheet of paper in it. If that is the case, you need to show the defect to the postal employee, try another envelope, and move on.
As for the rates, check out this website:
http://pe.usps.com/cpim/ftp/manuals/.../Notice123.pdf
This is a booklet that the Post Office puts out that should answer ALL of the questions you have about cost to ship. We use it at our office all the time, and have several of them around, just to make sure that we don't get overcharged. Some government employees are not the brightest, and some just don't know where to check to make sure they are giving you the right info. I recommend you print yourself a current copy, and take it with you in case there are any questions.
And finally, there are also INTERNATIONAL flat-rate shipping containers, too. The small international box was something like $12.95 to mail in December '09 when I mailed to England. The box size? About the size of a VHS tape. Pricey, but easy. And my local PO worker didn't know there was a "flat rate international". The printed booklet helped.
Odessa