I found this one way fare on the voyages-SNCF site for a Sunday in April (April 27 ’08) It will go fast! Catch it while you can. You’ll find that train ticket rates vary greatly, depending on when and how you buy your tickets. Here’s the direct link (while the ticket lasts)
Tip: Buy your tickets without reserving seats and it’s less expensive. You can also buy tickets without a specific date set when your ticket has no seat reservation.