I do think the OP is a bit of a special case. Surely we can't expect her to spend upward of $100 when she has already spent over $500 just to attend as it is interstate. I think the effort of spending so much and making so much effort to attend would be more than enough as a gift for me, I could not imagine being upset with a small gift or nothing if somebody travelled across the country and paid for accommodation to be with me at my wedding.
I personally believe people are becoming selfish. That is a mammoth effort for somebody else's special day. It isn't the OP's special day but she has still made a huge effort to go to see her friend marry.