It is possible to take a bus from Toulon to Saint-Tropez, but the journey is very long. It takes 1h45 mins to over 2 hours one way. It's not a favorite option for cruise passengers. You can find more information here.
Saint-Tropez is located about 70 kilometers from Toulon. A taxi ride takes about an hour. Expect a fee of € 100 to € 125 per taxi (4 persons one way).