Most people say to avoid RailEurope, a third party that costs more & does not show all the scheduled departures. Other than the actual train site you can also use the former Captain Train now, Train Line, https://www.trainline.eu, to book your trip. As an example I see on 3 June from Paris to Bayeux the prices vary from 20 - 34 Euros on 2nd Class & 22 - 41 Euros for First Class. There are even direct routes at certain times throughout the day.
Train Line has an App you can use & store your tickets on.
Enjoy your trip.