I just did the Normandy/D-D tour this past weekend. I was staying at the Pullman Montparnasse. I took the Metro (line 13) from Gaite station (actually a shorter walk than getting on the Metro at Gare Montparnasse). Got off at St. Lazare. It's only about a 12 minute Metro ride. I had previously purchased tickets on the train from St. Lazare to Bayeux. I took at train that left about 1:30 PM and arrived in Bayeux at about 3:30 PM. I went 2nd class but did buy a refundable ticket just in case FedEx dorked up my schedule. When I arrived at Bayeux (second stop on the train) I walked into town (10-12 minutes) and walked through the old cathedral. It's like a scaled down Notre Dame. And then also did the Bayeux Tapestry Museum (9 Euro). I grabbed some dinner at a restaurant in town then walked to the hotel where I was staying. It was the Premier Classe Bayeux. About a 15 minute walk from the meeting place for the tour I did. The name sounds impressive but it was a definite budget hotel. About $50 for a pretty small room and an even smaller bath. But I wasn't looking for anything fancy and it filled the bill. I made the reservation through Booking.com. The tour I took was with Overlordtour.com. I did tour #2 which was Omaha and Utah beach. It's a full day tour ending at about 6 PM. Cost is 95 Euro CASH. But it's a good tour and you can look on their website and where the tour goes and look at other tours if you're interested. They take your credit card but don't charge it, unless you're a no-show. I had a 7:30 PM train back to Paris after the tour and they will drop you off at the station or it's a short walk if you want to grab a bite to eat in town before you go to the station. Train got back about 9:40 and I was back in my hotel room by 10:30 PM.
It was a good experience and I was happy with the tour operator and like I said, the hotel met my needs (cheap and clean). Breakfast at the hotel was an extra 6 Euro. If you need more info feel free to drop me a PM.
MG2
One last PS. I just took a change of clothes and threw them in a backpack. There was not a lot of extra room in the 19 pax van we drove around in. I'm not sure where you would put a full size roll aboard if you brought that with you.