What is so cool about a diaper cake as a baby shower centerpiece is that it can fall in with any theme. Whatever your theme, you can easily make a diaper cake to fall in with it. What is more, making a diaper cake is far easier than you may think. You can even get videos that will show you exactly how to make one.
No, diapers are pretty expensive, I know, but the benefit to the mommy-to-be is so great that I think it is money well spent. If you take into account that many centerpieces cannot be used for anything else afterward, it puts the cost of a diaper cake into perspective.