you listed most of the top established french luthiers,
one can add Robert Bouchet (deceased) but guitars are very rare and expensive,
Daniel Friederich, Dominique Field, Michel D o n a d e y, Joel Laplane.
Giambattista are mades by Jean Baptiste Castellucia,
the Giambattista brand is for the "not too expensive models" and the Castellucia brand is for the high end models
I've played in the shop last week Giambattista Flamenca FG3 and Classic 60TH Superbs !!
So logically in the shop Giambattista brand should be the less expensive but it really worth it,
the others should be very expensive, these luhiers produced almost exclusively concert and grand concert guitars
may you give us some models and prices ?
It is in french but you'll find some picture of there work and i'm pretty sure the site owner understands english
http://www.guitareconcert.com/16901/272 ... on*id*val*
Check the luthier page links