How to handle SIL's destination wedding?

My DH and I just found out that his sister is planing to get married in Hawaii in about 6 months. The problem is we just filed for bankruptcy and short of living in complete poverty and putting every penny away, just for airfare, we can't go. We really don't want to borrow money from family members to go either. I'm just really mad that I am expected to spend all the money I've earned working a second job on attending someone's wedding, even though it is family. Any advice from someone who has been there??? I know this is going to blow way out of proportion soon...