Struggling financially with being a bridesmaid (Bach party)

As the title suggests, I'm struggling with how expensive everything is to be a part of one of my best friend's weddings. The MOH planned a 4 day destination bachelorette party without any discussions about expectations/budgets upfront. She's already apparently booked the airbnb, made dinner/brunch reservations and rented a boat. She has requested $587 from us upfront for the airbnb and boat. This total doesn't include cost of flights, meals, drinks, etc...... She estimated costs to be max $1,800

I simply cannot afford it and don't know how to go about it/what to say and it's really stressing me out. I would obviously love to celebrate the bride any opportunity I can but I just can't swing it financially.. Not to mention the cost of the destination wedding itself.. 💔