They are certainly more expensive than the discount airlines, but it comes close when you add up the costs of getting too and from the airport. I easily justify the extra euros for the half day saved by not hanging around in airports and security queues.

Also, book early for better train prices.

I did not want to call it out but yeah it seemed cheap to me too. I just did a quick research and 35 euros was the minimum I could find for Nice -> Paris on a third party website.

Ouigo TGVs are cheap.

Prices are about the same for the last 10 years.

Book early, check different departure times, or check Ouigo. It can quite cheap.