I purchased our certificates online through Hawaiisavers on Ebay for $215 a pair. I called ahead to make our reservations since we were traveling in peak time.
Although the helicopters take off from the airport, you check in at their office near Hilo Hatties. They shuttle you to the take off-site. Seating is prearranged by weight of the travelers, and each helicopter seats six.
We chose Kauai for the helicopter ride because of the NaPali coastline. It is only visible by air or sea. They videotape your takeoff and arrival and fill in with a typical air tour for your option to buy a DVD or VHS recording of your trip. They showed ours on the ride back, and we ended up purchasing it.
The ride is breathtaking. You wear headsets, through which the pilot explains what you are seeing and offers history about the island. Ours was a little light-spoken and sometimes hard to hear. There is no explaining the beauty of the view. Don't be disappointed if it is overcast on your scheduled day. Rain fills the waterfalls and adds in the sun for a rainbow. We saw a beautiful one, but I wasn't sure if my flash was turned off yet, so I didn't get a picture. You can really only take pictures out your one side, but most of the time, the pilot will face both directions before leaving that area.
Having done this once, I would not do it again, but I would recommend it for a one-time splurge.