The price for dance lessons at Gregoire and Alizee's studio is quite reasonable. From what I see in videos taken in the studio, Gregoire is the main teacher and Alizee seems to help out mostly in the front. I did see a few videos of other teachers in the summer program, but I imagine the two of them are around, so you might want to request Gregoire.
For a big fan, if you happen to be in Europe anyway, stopping by to take a few lessons might be a good idea. Beats just asking for an autograph. For the price of a few private lessons over a few days, you would actually personally know them.
Private Lesson - 36 €
Trial Lesson - 10 €
2 Lessons per week for a year - 266 €
http://www.danselyonnet.fr/tarifs.php