I am investing in the cheaper shipping method, which is to do it via internet at home, just haven't acquired the proper gear. Until then, unfortunately I have to charge that which is fair. For instance, today I mailed roughly 12oz (probably less) to 4 different address and it cost me $15+...I don't make the shipping charges sorry.
I recommend using PayPal to print shipping labels from home. You get a discount, plus cheaper tracking. All you need to use it is a PayPal account and a printer. Also, it won't cost more than $4 to ship a single book via USPS media mail, whether you take it to the post office or ship from home. More info: https://www.usps.com/ship/media-mail.htm