Single on Eurostar to Paris - £39. Lots of choice on times to depart. (I looked up coaches but that was a little more expensive and lots longer.)
Visit something you've always wanted to see in Paris
Train to Lyon - £20.50 (That was TGV and around two hours. There may be cheaper and a little slower Co-rail)
Train to Le Puy en Velay £19.50.
Do-able in one day if you wanted to. Opportunities for the interesting encounters which makes travel (and pilgrimaging) enjoyable as well as for stretching your legs in Paris and Lyon, eating freshly made baguettes or similar, looking out of windows at fields and forests, factories and back gardens, etc.
Take the cheap flight if you are in a hurry, but I find that even though the actual time in the air is so short, the whole package - getting to airport, going through security, queuing up to board, getting off the plane and through arrivals, finding out where the bus goes from to the city etc - makes me just as tired as a day's travel, without the enjoyment value of the journey.
(and being able to take, in my case, my father's little penknife which I keep in my purse to sharpen pencils, open plastic packaging etc, and live in dread of forgetting to take out before a plane journey and having it confiscated, or else forgetting where I put it safely at home while I was away)
But maybe I'm just a romantic about train travel ('there's something in my eye') and an idealist about considering the least carbon option when possible.
Bridget