JEM -- check out Bruce Voyles auction website
http://www.jbrucevoyles.com/. Ralph Bone folders (and fixed blades) do show up there once in a while, and yes, the do sell for several hundred each time. Compared to today's folders they are very plain, obviously meant to be working knives, not show pieces. But as there are those of us who appreciate the quality of Bone knives, they continue to be collectible. I wouldn't recommend them as a source for your retirement fund, just never know if they will continue to appreciate in value, but one or two would be a very nice addition to any collection.
The last I had heard of Ralph before his death was that he was doing some gunsmithing, but no longer made knives.
Hope this helps,
Mike