Here's a map of French airports:
http://www.mapsofworld.com/international-airports/europe/france.html
. . . and here's a list of all the airports suitable for travel to the Ardeche (from the region's official tourism website):
Nimes is only served by Ryanair, from Luton and (seasonally) from Liverpool.
Lyon is served by BMI Regional from Birmingham & Manchester, by BA from Heathrow and by easyJet from Edinburgh, Gatwick &Stansted.
Grenoble is served (seasonally) by easyJet from Birmingham, Bristol, Edinburgh, Liverpool, Gatwick, Luton & Stansted, by FlyBe from Southampton, by Jet2 from Leeds/Bradford & Manchester, by Monarch from Birmingham, Leeds/Bradford, Gatwick & Manchester, and by Ryanair from Stansted.
Marseille is served by BA from Heathrow, by easyJet from Gatwick & Bristol and by Ryanair from Edinburgh, Stansted and East Midlands.
Avignon is served by FlyBe from Birmingham & Southampton, and by Jet2 from Leeds/Bradford.
Book as early as possible!
Chris