Saint Malo can be reached in about 3h30 from Paris by Toll hyway A11 to Rennes (2h45), and R.N. 137 (from Rennes to Saint Malo).
Saint-Malo is 2 hours away from Caen (north west), Nantes (south west) and Brest (most western part of Britany).
Highways in Britany are toll free.

Driving distances to Saint Malo

Bordeaux 511 km 5h00
Brest 220 km 2h30
Lille 538 km 5h45
Marseille 1152 km 10h15
Nantes 190 km 2h00
Paris 419 km 3h30
Quimper 200 km 2h40
Rennes 73 km 0h45
Saint-Brieuc 75 km 1h00
Strasbourg 901 km 8h00
Toulouse 756 km 7h00