When decorating a kid's bedroom, you don't need a big budget to do it up. To start, don't buy furniture marketed for "kids." This seems to always be more expensive. Kids furniture gets a lot of wear and tear so save big by reusing older adult furniture. When buying used, just be sure the item hasn't been recalled and meets all current safety requirements.
Search your home, local classifieds, yard sales or online shopping and auction sites. One of my favorite places to find great furniture for any room is the "free" category on CraigsList. Don't worry about the color or hardware; just look for something structurally sound and the right size for your room. Once you get it home, give it a quick sanding and a coat of paint. For bureaus and armories you can add some fun hardware found at your local home improvement store. Or, get creative and use something like small souvenir baseball bats for door handles on an armoire.
You can also use your creativity with a bed. For a little girl, skip the head and foot board altogether. Hang a mosquito net on a hoop from the ceiling and drape it around the head of the bed for a princess effect. Don't forget a side table to hold a good book and alarm clock. Make an old storage night stand from the 70's new with a fresh coat of paint and free hand or stencil a monogram in one of your accent colors on the front.