Day trip from Saint Malo to MSM

By way of Rome2Rio.com I found a website for Keolis-Emeraude, a company that runs buses to Mont St Michel. The website doesn't extend beyond June 2017, but looking at the calendar, it appears that there is no service in January.

There may well be bus tours running from St. Malo, however.

You can take the train also St-Malo to Pontorson—Mont-St-Michel on 5 January and then the bus is sitting there to take you to Mont St Michel. Very obvious you will see other tourists

We did this trip in May of 2017. As our requirements were a bit different, we took a taxi both ways, which is ridiculously expensive. About $60 euros each way.

Because it was basically a photographic trip for both of us, and we very much wanted to catch the morning and evening light, ed decided it was worth it for our purposes. We it not for that requirement, we would have used the aforementioned bus.

If you get there before the tour busses and later walk around after they have left, you can have the entire site basically to yourself. We spent the night on the island and it is so spooky at night it gives you the creeps. It was a ghost town after 6:00.

Walking the battlements, it's going to be very windy and cold.

Thank you all for your advise! I will try to find out more about the train option but it is good to know that a taxi option may be available if public transport doesn't work out. I wasnt sure that was possible or even at the cost quoted an option. I really don't want to hassle with a rental for such a short time. Honestly, time is more valuable than money on this leg of the journey...within reason...I really want to see Mont St Michel!

For point to point public transport is to prefer but a car will give you the flexibility to explore the surroundings too. The coastal road from St. Malo to Cancale is very scenic. From Mont-Dol and more higher points you can have a panoramic view over the lowlands with Le Mont-Saint-Michel at the background. Driving back to St. Malo you can drive along the border of the Rance estuary and visit Saint-Suliac. Sunset is very early in January so you can drive back to MSM again for it and hopefully the place is around that time of the year illuminated too.

Have to say my visit was in June a few years back, so with the weather in January it can be a whole different experience, especially if it hopefully not rains.

Thank you, Wil. You raise good points.

There are few shuttle buses from November till March between St Malo and MSM. Over a few days in winter, there is one round trip leaving St Malo at 9:15am and coming back at 5:00pm (for example on January 3rd and 6th) for 23€/person.
The other solution with public transport is to take the train from St Malo to Dol, change train to Pontorson (or take a bus Dol to MSM when possible), and then a shuttle bus to MSM. It means shifting transport quite a few times for the round trip, and then a loss of time without seeing the coastal road or enjoying other stops along the road.
Of course, renting a car, taking a taxi or a private tour gives you more freedom and opportunities to discover not only MSM over the day.