The best price found from United States to Sulawesi is on January 18th, 2016, travelling with Singapore Airlines. See more options, compare prices and book: search flights.
Silk Air flies between Manado and Singapore a four days per week for S$567 (one way). Air Asia has daily flights from Makassar to Kuala Lumpur for around Rp1,400,000 each way.
The three transport hubs are Makassar and Manado, which are well connected with the rest of Indonesia, and Palu, which offers connections to Balikpapan in Kalimantan. There are direct flights to Java, Bali, Kalimantan, Maluku and Papua. Merpati Nusantara Airlines, Garuda Indonesia and Lion Air are the main carriers, but Batavia Air, Sriwijaya Air and Wings Air also service a handful of destinations.