I've stayed at many Formule 1 hotels in France, including the one in St. Malo. It's cheap, basic and has free parking (not secure). It doesn't have a restaurant and is based on an industrial estate so might not be much to choose from in the area. Hotel in SAINT MALO - Book your hotel hotelF1 Saint Malo
We stayed on two separate occasions at the Chateaubriand in St. Malo- it was wonderful with everything within walking distance but parking is difficult but not impossible. Hope you will have time to walk around the cite - fabulous place.