Here is another 18 inch doll bed option.
We purchased a folding stacking shelf from WalMart for under $6.00. No assembling required.
Next, we placed a doll mattress (homemade of course) on top of the frame (after folding it out), and made our doll bed as usual.
The shelf is ideal for a single bed setting. Later, if space is a problem, simply fold every thing up and put it away. Similar stacking units may also be found at other stores... (cost may vary).
If you are working with a budget this holiday season, this just might help you to stay on target.
Happy Crafting :o)