a VirtualTourist member from Regina
are bus lines available from Caen to MSM?
Unfortunately the short answer is no. You can get a TER train from Caen to Pontorson and then a shuttle bus from the station to the Mont. The only hiccup there is there seem to be only 3 trains a day, at around 7h10, another at 14h00 and another after 17h00. Here is the link to have a look at times and prices. I used the 15th May just as a try. :
These are TER trains so need no reservation beforehand. You might find it almost as cheap to rent a car for a day, from Caen you have a double carriageway right to Pontorson which is just 10 kms from the Mont, and is free, no motorway charges.