The ISBN number ties into a catalog of all (registered) books in print. This catalog lists the publisher, access and purchasing information, and descriptive data about each book. For that reason, the publisher needs to apply for the ISBN number.
Click here for a copy of the ISBN application for a single ISBN number for $125. Note that this application is not available online at the ISBN registry agency.
When you apply for an ISBN number, you can also request a corresponding Bar Code for an additional $25.00. You can put the price of your book in the bar code or you can omit it, whichever you prefer. Unless you are confident in your knowledge of the market, we generally recommend that you omit the price. Then you can change it -- up or down -- depending upon your experience selling your book.