If you want a slightly odd and rustic experience in Paris, check out ChantAirelle in the 5th. It's a simple restaurant featuring recipes and products from the Auvergne, plus a bit of touristy stuff stuck on front. Don't fear though, the staff is friendly and the cooking is good. Nothing we had was subtle; this is casual mountain food. But the potatoes and cheese dish was tasty with a delicious thin sliced ham. My "salmon trout" turned out to be salmon prepared as if it were a mountain trout; a bit bizarre, but good.
I'd say this place isn't worth a particular trip, but if you're tired of the Parisian experience you can get a bit of Auvergne feel for a cheap price. Nice outdoor space in back, too.