Heck, It really isn't that hard to build something up if you can find leather that is thick enough. I rebuilt a seat with almost no idea of what I was doing and it turned out fairly well on the first try! The biggest problem I ran into was that I made the new leather a little too long- The old leather that I used as a template was stretched and the new leather was more supple and stretched some after installation. With the leather and rivets it was about $25.00, mostly spent on the rivets and the tools that went with them.

There are several threads on this site including mine that talk about rebuilding Brooks saddles. The expert dude on this site is rhm. I think he's got several threads on the subject. He does really good work BTW...