The itinerary lasts 3hrs 15min, and has 1 steps, and it will cost 12 euros minimum.

Nantes - Jonzac
The step from Nantes to Jonzac lasts 3hrs 15min. You'll travel in a INTERCITÉS operated by SNCF Voyageurs.
On board, you'll have access to: Drinks and snacks, Wi-Fi, Bike.
You can find tickets from 12.9 euros if you book 2 months in advance.