If you have a guest bedroom but no bed, you can pull it off without spending lots of money on a bedroom set. A simple mattress and boxspring on a frame would do. Or you can add one of those air mattresses that are as high as a bed.
There's really no need to buy a footboard and headboard any more. There are plenty of creative ways to make an interesting headboard. Here is one. A long shelf, a reclaimed mantel or even a pretty curtain rod can hold a long cushion, tapestry or other fabric to become the backdrop for the bed. It acts as wall art as well as "finishes" the look of the bed.
As for the foot of the bed, you can add a bench, chest, or long ottoman for a spot to sit or hold a decorative arrangement like a serving tray with books or a tea set.