It would probably cost about $25.00 each way plus tip. Depending on how many are in your party it might be cheaper to use Mears. They have a shuttle that costs about $12-$14 per person round trip.
We rented a car for the day and the cost was about $45.00 including tax, this was better for us as it gaves us more freedom to leave the park when we were ready and not have to wait for the shuttle or get a taxi.