This thread comes up every year.
Like so many other questions that are regulars on MN, it is all about the communication.
Inviting someone to something, then presenting them with a bill afterwards that there had been no mention of before is utterly wrong.
Equally, expecting one family to host every year - to do all the work before, during and after the event, and be expected to pick up the bill for what sounds like a lot of people ("all the cousins, grandparents" and one presumes OPs siblings / sibling inaws) is also very wrong.
Only hearing it from the OP's stance, it is possible that your sister might have done better to communicate this better..... maybe last year when you were all thanking her for her hard work, she could have mentioned then how they can't really afford to pay for everything as well as host each year, she could have said "Look, I see traveling wise it makes sense for everyone to come to us, but that is impacting us a lot on the cost, so maybe next year we can work out an approx cost per head / or per family and everyone contributes more fairly?" type conversation. BUT why haven't you, your parents, and other siblings been offering that in the first place if you always go there ?
YABU.