kittygirl I'm not sure if sisal is a special kind of rope or just what they call it. Before I got my kitty I read a lot of stuff on the net to prepare, and kept seeing the word sisal used to describe scratching posts, so I searched for that in ebay and poof found tons of condos etc.
If you do the ebay thing just be careful and read the whole ad so you know exactely what you are bidding on...and be patient, if you only want to spend say $100. max on something then another $50. max for shipping, don't worry if you're not the winner because the same thing, or at least close to it will be up for auction sooner or later.