Book high-speed trains early, and look at Ouigo

TGV fares climb as the departure date approaches, so the Paris–Lyon or Paris–Bordeaux trip that costs little when booked weeks ahead can cost several times more the day before. Ouigo is SNCF's low-cost high-speed service: the same trains at lower prices, but with strict rules on luggage and boarding times, and some departures leave from stations outside the city center. Check which station before you book.