I've paid my copy for around 400 € five years ago in France.
It is quite the only detailed book on Voisin cars (apart from the two book Gabriel Voisin has written on his planes and cars, and a weird picture 'file' made by René Bellu).
Still, as far as I know, according to Voisin enthusiasts, this book is not very good, unfortunately ! Apparently, there are countless mistakes in it...