I finally have all six volumes. It took over two years to get them and I had to finally hire a book finder.
All together I paid about $2,000 USD to get them. I still can't believe that I ever put that much money into books. Because I got them over time, the amount didn't seem so bad. It was when I added it all up, I was in shock.! That makes them about $335 USD each. Of course there was the finder's fee and the shipping and handling from Europe and these books are HEAVY!
I have been advised to insure them for about $2,500 to $3,000 in case anything happens to them. I was also advised to put them in my will and to make sure that a book appraiser is named to appraise them when I pass them on.
I don't suppose that they would have cost half so much if M. Ferrand had not died so young. With the death of an author, the price of his books goes up.
I hope that those of you who are still looking can find them for less. If I had to do it all over again, I would probably not do it.
Perhaps they will be my bequest to some library some day, or perhaps someone who wants the full set and doesn't mind spending a lot will buy them.