My husband and I created one using those flat plastic sleds you can buy
at toy stores.  In a particular doorway, we needed to use two so we used
double-sided carpet tape to hook them together.  You then cut them down
to fit around the door frame.  This is a very cheap way to make your own.
The sleds usually run around $2-3.
 
Melanee Ellis
"The Ferret Lady"
www.ferretlady.org
[Posted in FML issue 4244]