10 Things (Under $100!) That Can Transform a Room

5. Wallpapering the interiors of your bookcases creates the illusion that they are deeper than they are, making the entire area seem bigger. Oversized prints do this the most effectively and, as Galli says, "are a small detail that goes a long way for the design-savvy and the observant. I love the mystery of pulling a book out and finding—surprise!—a bold color or beautiful design."

Estimated cost: $90