New intra-Hawaiian carrier Go! is extending its $39 fare sale through the summer months. $39 gets you a one-way ticket between Honolulu and either Lihue (Kauai), Kona (Big Island), Kahalui (Maui) or Hilo (Big Island). This is about half what it used to cost to fly between the islands. Book by May 7th for travel between June 9th and September 30th.