Venue

We are planning on having the ceremony on the beach at Robert Moses. We need a packup plan that is free or inexpensive if it rains. We have thought about parks with nice gazeebo's or a nice hotel or something. We need help. The problem is if it doesn't rain and we need a deposit for the dry area we will lose it. The wedding is on July 9th. Thank you for any ideas whatsoever. We are very easy. There will be about 23 people. Best if it is in Town of Babylon, Town of Oyster Bay, south shore?