Paris - Bayeux - MSM - Loire Valley - several transportation questions

Your plan sounds lovely.

There should not be any drop-off fees anywhere in France. If you find a rental company that wants to charge you for a one-way trip, find another rental company

Unless there are other considerations you have not mentioned, I would make the decision about when to tour Caen based on where you find the desired rental. That is, a car you like from a company that charges no drop off fees and has offices in the city where you want to leave the car at the end of your rental.

If this is available from both cities, see Caen enroute to Bayeux just to avoid the small amount of doubling back. but its a small difference logistically.

As for MSM, I think your idea of driving there is best, but there is slow infrequent local train service (sometimes with a bus I think) from Caen. The station is Pontorson. The connection to Amboise is similarly laborious, but feasible.

You'll want a car in the Loire anyway.

Finally, you could bike to Pontorson, perhaps with an overnight along the way. Many bike rental shops will pick up bikes from a remote location, deliver bags to hotels, and provide similar self-guided services for a fee.

I think your original plan is very good though.

Caen is much bigger than Bayeux so it offers more alternatives. There are car rental offices near the station. If you are interested in WWII, the Caen Peace Memorial earns good reviews. You sound like you prefer to do things yourself, but Google will show you that there are day trips from both Caen and Bayeux to Mont St-Michel if for some reason you decide against driving there.

If you're interested in a WWII museum, the best one imo is the one in Bayeux. It is less crowded, less chaotic, better organized and less expensive than the one in Caen which we did not enjoy.
We've rented cars in Caen several times and once in Bayeux. I'd go directly to Bayeux and rent the car from there after your bike tour. Or, bike to Pontorson as Adam suggested, but I would not bother with Caen. While you have more choices in Caen, me personally, I wouldn't want to waste my time going back to Caen then on to MSM from Caen, passing Bayeux again. I'd rather just leave from Bayeux and skip Caen altogether. Caen is a large city, is not charming and not worth any time imo.

Well, normally I think Susan is right about everything, but I have to disagree about the Caen Memorial, a superb WWII museum though pricey. It's worth seeing if you have time, in addition to Bayeux and your other destinations. But don't trade Bayeux for Caen, overall Bayeux has more beauty and interest.

I'm thinking that one reason Caen is "not charming" is that it was totally levelled in WWII.

Have you considered returning the car at the [Tours]St.-Pierre des Corps TGV station, if you're going back to Paris at the end?

Rick mentions the idea (he's talking about Rouen, I think) of getting off the train, locking your luggage in the [fully enclosed?] trunk of the car and leaving the car in the major rental company high-rise garage, and seeing a city before driving off hours later. Naturally there is risk involved, and I don't know how you can learn which rental companies have a very secure garage, and which (like in St Pierre des Corps) just have wide-open, street-level lots.

While we didn't feel that an overnight at MSM was required, many posters here swear by it. I wonder if the Hotel Churchill van service would accept your luggage and you for a one-way trip to MSM, instead of the usual round-trip. You could get a cab to a rental agency near MSM, if there is one. It's quite a touristy (descriptive, not a slam ... Crocodile Farm, for example! ) highway area.

We had a car, and went in the other direction (Tours-Chinon-Dinard(&MSM runout)-Bayeux-Paris). But I'm not flogging that route. I do want to observe that if you have reserved the time for a leisurely drive, there are plenty of attractive short visits along the way. We didn't have time for the Cider Route, but we loved Dinan, some estate public gardens, Vitré, Dol de Bretagne. I remember being disappointed with Coutances, and the time to drive there. We skipped Caen. Although I think bicycles are a great idea for the Bayeux area, I would be careful about narrow paved roads and heavy auto traffic near the D-Day sites.

Dick, sorry to disappoint you... I'm definitely not right about everything... just ask my son... : ) .. I try to only write my opinion based on having been somewhere because I want others to have a good time and spend their limited time wisely, and I really disliked that museum.

I've been to all of them more than once and liked them all very much... the only exception was Caen.

Thank you so much for all the helpful replies. Lots to digest, but planning is a large part of the fun!