For anyone else that's curious about a comparison in the US, I looked up Amtrak from Atlanta to Washington DC, roughly the same length. $109 ticket and it lists just over 14 hours to travel. Based on what I've read it's practically guaranteed to take a good bit longer though.
So ~75% higher cost and at best ~75% longer travel time.
"Starting at" means if you book 3 months in advance and are lucky to get one of the rare discounted tickets. Normal price is probably the triple of that or so.
There are 11 viable trains that connect Berlin with Paris during the day, with up to 2 transfers. During the night, there's a sleeper train connecting the two cities 3 times a week