Are there more than one type for 4x5 Crowns?
Are they available? and any idea how much, well roughly.

I don't know of any variation during production with the fresnel lens for a 4x5 Crown or Speed.

Check ebay, they come up fairly often.

The standard fresnel seems to work pretty good, and it provides the proper spacing the back was designed to have with regards film holders. there seems to be many options available, some GG replacements can do horrible damage to the pocket book, whereas putting the money towards a lens upgrade will at least show up on one's film. The Century doesn't have a fresnel, nor do many cameras, and they work just fine, but I like my Crown fresnel best of all my cameras, though there are probably better out there.
regards,
Stephen

I fitted a fresnel to my Century w/o any mods to the gg frame, so it is possible to do. YRMV.