If you don't have a credit card or prefer to not use them online, you can use the blue "PayPal Checkout" button in the Shopping Cart to pay securely. 

If you wish, you can always check directly with the bookseller listing the item to see if they are willing to accept a check or money order. You can use the "Ask the Seller a Question" link under the price information on any book detail page to write them an email. You can also find their contact information by clicking on their shop name on the book listing.