Sweet as Baby's Breath
Done well, baby's breath can make a beautiful and affordable centerpiece. Personally, I only like baby's breath when it is alone, as shown in these arrangements. Bundles of baby's breath create a fluffy fragrant cloud. If placed on top of a glass vase, it will look like it is floating. For a more dramatic impact, arrange the baby's breath in a solid, ceramic piece.
Photos from Project Wedding, The Cinderella Project, and Chillipit
You can also repurpose your centerpieces as ceremony decor (as shown below in this photo from The Knot)