Aloha,
I am a wedding photographer on the Big Island. There are so many public beaches you can get married on, including the Four Seasons. Every resort has to have public access to the beaches by law. There are some great wedding coordinators on the island, personal one on one that can tell locations, etc. Depending on how large your wedding is, a lot of it can even be done by yourself. A 50% deposit is fairly common. I know for my photography services I have a 30% deposit.
Best,
Bob