I have visted most of the aerodromes/airports in the area as I am thinking of flying down from Biggin in my VansRV6.
Montpellier main airport LFMT does have several light aircraft in various private hangars, ( one of them is full of Vari-Ezes ) so it is possible to fly in there.
Montpellier Candillargues LFNG, is a great GA airport just to the west of the main airport -- loads of light aircraft and home builts.
Bezier LFMU is to the west of Montpellier by about 50 miles -- a bit desolate with a few Ryan air flights with taxi's only at the arr/dep times.
Millau - LFCM is a long way north and IS a GA airport with hotel on sight and right next to motorway.
Saint Martin de londres - LFNL is NW of LFMT and very desolate and in the hills.
Bedarieux - LFNX is again very desolate north of Bezier.
At least at the main LFMT airport there is car hire and customs.
Look up the SIA web site for all the approach plates and info.