I read Tim question and will keep your answers in mind but I need some other help. I arrive in Lille on Sept 9, touring Vimy and then I want to see Dieppe, Etretat, Caen before I take tours of WW2 from Bayeux. Any suggestions without going to Paris. I am travelling alone.
I haven't been to any of the places on your list, but I did some Google searches. There is hourly direct train service between Lille and Arras. For most departure times, going from Arras to Dieppe by train would mean backtracking to Paris. There is no train station in Etretat. I couldn't find out anything about bus service between Dieppe and Etretat or between Etretat and Caen. It looks to me like your best option for easily getting from place to place woudl be to pick up a rental car in Lille and drop it off in Caen or Bayeux. The car rental agencies have offices right by the train station in Caen, but in Bayeux the offices are not close to the train station.