trains

The best site to get tickets is from the actual train company itself, SNCF.

https://www.sncf-connect.com/app/en-en/home/search/od

Sometimes people find the website awkward or it won't take your credit card, in which case I use www.trainline.com This is a 3rd party site but it's reliable.

The least expensive tickets SNCF offers are called “Prem’s” tickets, which can be 75% less than tickets bought at the last minute. For 3 months from today there are TGV tickets from Paris to Lyon for €25. They go on sale 90 days in advance of the train’s departure date. Be sure to mark your calendar so you can buy your tix on that date. The Trainline also will have them for sale.

Besides SNCF, Trenitalia also has trains on the Paris -Lyon route, and they're often cheaper than SNCF. So check Trenitalia as well.

For all of your train questions across Europe go to seat61.com.

Trainline.eu. is very user friendly. You can always go to SNCF to book after sorting it out on Trainline -- I use trainline because they also reliably make the tickets easily accessible.

Trainline (the European version, not the UK version) was originally called "Capitaine Train" and was set up by a couple of French guys unhappy with the SNCF booking system (which that time couldn't even book connections). So they created an alternative, were successful, and were bought (and rebranded) by Trainline.

They are useful in my opionion for tickets in France, Spain and Italy, and between these countries. Advantages are that they understand the english version of European place names (try finding Florence on Trenitalia...) and more importantly that they show all operators on routes where there are more than one. We are increasingly seeing competition between different companies on major routes. Soon RENFE plans on running trains on Paris - Lyon - Marseilles route as well. So that will mean three operators to choose from between Paris and the Southeast...

Trenitalia has Lyon-to- Paris tickets for as little as €20 on its Frecciarosa trains taking about 2 hours. TheTrainline shows dates in May that were $11.34 on its site.
Now, THAT, is a deal!
You gotta love the EU for bringing competition to train transportation and how it’s bringing the public lower prices.