If you use a link checking program such as
Xenu's Link Sleuth, you'll find that a site map is automatically generated as part of its reporting facility. They often need some editing, but for a quick simple and cheap (free!) method, it's pretty hard to beat! :o)
There's even a webpage that walks you through the whole process - wouldn't you just know it! :o)
Build a Site Map for your Website - An Explanation
HTH!
Paul