Access to the national park is by guided boat tour only, and numbers are currently restricted to 600 people per day (a quota that is often filled). Day-tours from Princesa are P1500 per person, departing at around 7.30am, and including all fees, a basic lunch buffet on Sabang beach and a short time for swimming. If you want to stay on in Sabang they’ll drop you off after the tour. Renting a whole van for a day-trip to the Underground River will be at least P3500.
While taking a tour is the most convenient option, it’s much cheaper to arrange a visit independently, especially if you have a group. You’ll need to take a minivan or jeepney (2–3hr) to Sabang Wharf from the San José Terminal in Puerto Princesa; at the wharf’s Tourist Assistance Information Center you can buy the permit (P200/person) required to visit the national park, and arrange a bangka (P700/boat, return trip) to take you to the entrance. Because of the quota, you’ll need to get here early. Your permit includes the cost of a guide and the second boat into the actual cave. To save the bangka fare you can also walk to the cave from Sabang.