Pledge levels at the $15 amount or higher say that you will have the option to purchase a soft- or hardcover copy through DriveThruRPG.
What this means is that when the book is done, you'll get a discount link that allows you to buy the book through DriveThruRPG's print-on-demand service at the cost it takes them to print and ship it.
The cost depends on if you get the hardcover or softcover, and whether the art is black and white or in color. Here are some estimates on how much it will cost to print and ship:
Softcover B&W: $10
Softcover Color: $14
Hardcover B&W: $15
Hardcover Color: $19