As is now usual for us, when we went to Paris at the beginning of the month we went by bus and train: bus from Preuilly to Tours, train from Tours to Paris. The bus cost us the princely sum of €1.70, the train €17 each.
Ken asked last year how we manage to find such cheap train fares. Our secret is to book early - the tickets become available three months in advance, and as there are only a certain number of cheap seats on each train these tend to go early for the popular times. We prefer to catch the bus to Tours, and unfortunately, the bus coincides with the popular train times.
If you have some flexibility getting to the station (or are prepared to hang around in Tours for a couple of hours) there are nearly always some €17 each way seats available, even for the next day. The trick until now has been finding them.
Recent changes to the SNCF Billets site has made finding them easier.
You start by entering the Stations (or towns) you are travelling between. Then just put in the date you want to travel, and check the "Trouvez les meilleurs prix sur un mois" box and click the Rèservez button. On the screen that comes up choose the day you want to travel. This will show you all the fares available for that date, then all you have to do is scroll down to find the cheap one. Usually for us it is the last train of the evening (which arrives in Paris at 11.00pm), but even a few days before you travel there are often tickets available on the midday train.
When travelling from Tours Central to Paris it is often cheaper to buy a ticket from St Pierre des Corps and just purchase a navette ticket (€1.20) between Tours and St P.d.C. on the day: when I was writing this the cheapest fares for tomorrow from Tours to Paris Montparnasse were €31.50 whilst from St Pierre des Corps the cheapest were €17.00.