You might want to check out the site http://www.sncf.com

It will give you times and costs for Paris trains. You can also book your tickets online without a credit card. You get a reference number that you show at the train station and pay for them there. I have used a number of times and it makes booking tickets a very easy and convenient.

As for Lyon I plan to go with a friend in early May for day also. Still it is a long trip for a day from Paris. Hope this helps.

Tom Cobban Grenoble,France