When figuring pricing, remember shipping material costs.  If you choose to send your books via USPS Priority mail, you can order your boxes and tape free of charge directly from the post office online at http://www.usps.com.  Find the shipping materials area and the boxes, tape you need, the “price” is $0.00.  There are stipulations you’ll need to adhere to that are listed on their site including you must use these items for priority class only.