I second Virus's suggestion. A front opening enclosure with a lock would be essentially kitty proof and large enough the last the dragon his or her whole life.

Just a thought, but have you considered adopting an adult? A cat would have a hard time eating a full grown beardie, and there are lots of them out there looking for snuggles and love. It totally depends on how far you are willing to go, etc, but there is a store in Acton, MA that has many adult beardies up for adoption for little or nothing. A lot of humane societies and shelters have them too.