As you can see on the map if you zoom in a little, the nearest train station is Lus-la-Croix-Haute. The trip from Grenoble takes about an hour and a half, it should appear as a result on the SNCF website, or you can see the timetable here. Depending on whether you will have heavy luggage etc., you should be able toTo reach Vaunières on foot from the station, otherwise maybe you could use a taxi or a car rental, I am not able to find any public transport option.