nrr is correct about the website. I see it for €36 on a random day in April. But nrr is wrong to say that Part-Dieu is not in the center. Both Part-Dieu and Perrache are in the center of Lyon. But neither are in the true heart of the old city or Bellecour. They are both a short walk or taxi ride away. And the airport train only goes to Part-Dieu so you would have to transfer to another train to get to Perrache anyways. Plus they have been closing the tracks to Perrache recently for renovation of the line.

Where exactly are you going in Lyon?