Send it by "media" mail. You can look this up online, estimate your postage, but nothing but the book, no advertising allowed.
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http://www.usps.com/send/waystosendm.../mediamail.htm"
Send your printed or recorded material using this service.
Media MailŪ service is a cost efficient way to mail books, sound recordings, recorded video tapes, printed music, and recorded computer-readable media (such as CDs, DVDs, and diskettes). Media Mail can not contain advertising except for incidental announcements of books. The maximum weight for Media Mail is 70 lbs.
There are presorted rates available for bulk quantities of Media Mail (minimum quantity is 300 pieces).
A barcode discount is available for Media Mail.
Rates are based on weight and size.
You can go to this page and it will direct you to the next page to calculate postage.