I just wanted to expand on what a few others have mentioned about saving the date cards.
I have a friend who lives in Washington and had told people she was getting married, which helps to spread the word so people at least know that you're engaged and are planning to get married.
About 6-8 months prior to the wedding, she sent little envelopes out to anyone who was out of town (which was almost everyone). She's a graphic designer so she was creative in doing this and put it on several little cards, but basically it said they were getting married on such-and-such date at the specific place and they would be sending out formal invitations later, but they wanted to allow people from out of town enough time to plan if they were able to join them (but would understand if we were unable).
It mentioned the nearest airport, and that the wedding was taking place on an island and how to get to the island (I can't remember if there was a bridge or you needed to catch a ferry). They had arranged special rates at several hotels of varying rates and mentioned the hotel nearest to the location as well as other hotels in a more populated area since the wedding was in a relatively remote location.
And please do not feel at all guilty about travel costs. I have been to weddings on other islands as well as in other states and have never once given a second thought about the costs.