If you're handy with tools you can build one from a used end table or wood.
 
I made Noah and Allie beds out of table legs, a small sheet of plywood and some 1x3's 
These are fence posts, cut in half 
http://i1199.photobucket.com/albums/...n/579af509.jpg  http://i1199.photobucket.com/albums/...n/41bae743.jpg  
these are table legs, ready made from home depot and turned upside down. 
http://i1199.photobucket.com/albums/...n/43469e68.jpg  http://i1199.photobucket.com/albums/...n/a57dbfed.jpg 
I used handkerchiefs for the cushions ( 2 for .99 at the dollar tree). Noah chewed on his a little but a light sanding took care of it.  They climb on them like monkeys but can't move them around.