I think Big Horn makes a cordura with a Ralide tree. Their synthetics tend to hold up over time unlike some others. If you are riding a lot though, you probably want to stick with leather. I hate to say it, but most older saddles are going to be made better than the new ones especially the Circle Y's
My saddle has a Ralide tree and it fits both my horses pretty good. People like flex trees because they fit a wide range of horse without adding more pad. I don't really like them because I feel like they move too much underneath me (I know it's hard to explain)
These are some links that might be of interest to you.
If you buy used make sure you check the tree out before you buy.
What Are The Different Types of Saddle Trees? | eHow.com
Buying a Saddle - How Can I Be Sure The Saddle Is Safe?
Saddle Fitting: Free and easy saddle fit help from the experts