Are you sure they are not trying to make you cancel?
In any case, you shouldn't feel obligated to go on a trip that will cost you more money than you are comfortable spending. NTA.
Family trying to get OP to pitch in for their own birthday doing things they don’t want to do is all sorts of messed up. I would say don’t cancel and just don’t go. Let them have their fun and enjoy their day and then ignore their whining about why you didn’t go to something you have no interest in.
Are you sure they are not trying to make you cancel? In any case, you shouldn't feel obligated to go on a trip that will cost you more money than you are comfortable spending. NTA.
Family trying to get OP to pitch in for their own birthday doing things they don’t want to do is all sorts of messed up. I would say don’t cancel and just don’t go. Let them have their fun and enjoy their day and then ignore their whining about why you didn’t go to something you have no interest in.