Hitchhike

It's free, takes about 7-8 hours from Geneva and you can practice your French to boot!

If that's not your thing, then you can also check out some ride share sites:

French: http://www.carpooling.fr/
German: mitfahrgelegenheit.de (but you can find rides through France and Switzerland too)

I've always found nice people there.. you share the cost and it's faster than any train not heading to the South of France.

Good luck!