Most resorts can organise snorkelling trips, either to specific destinations the group requests or to a set route determined by the resort.
Generally a snorkelling trip will require a minimum of four people (or at least four seats paid for) and will come in a half-day or full day flavour. Prices vary considerably -- both according to the resort and to the distances involved -- as does the quality of the snorkelling. Full-day trips generally come with lunch included.
We paid 70,000 rupiah per person (for four people) at Kadidiri Paradise for a trip that covered Jellyfish Lake, Karina Beach and Taipi Island, while Black Marlin charges 500,000 rupiah for a half-day trip and 750,000 rupiah for a full-day trip (maximum of six people).
At the more expensive Island Retreat, snorkelling trips ranged from 175,000 rupiah per person for a three-hour trip to one site, 200,000 rupiah to Pasir Tengah Atoll (roughly half way to Una Una), 300,000 rupiah for a six-hour trip to Pulau Taupan, visiting two or three reefs, through to 350,000 rupiah for a full-day trip to Baturando (around on the southeast coast of Pulau Batudaka) -- all based on a minimum of four people.
All trips should include snorkelling gear, though some may charge a surcharge. If you have specialist requirements for your equipment, bring your own.