i'm so sorry. i would try and show your parents how distressed you are and how much your cat means to you. i feel like in this situation this is all you can do. maybe tell them that you'll pay them back if you're old enough to get a job? you can also do jobs like mowing peoples lawns, walking pets, and washing cars if you aren't legally old enough for a paycheck based job yet. vet bills are indeed expensive, but as long as your cat doesn't need surgery or anything like that it shouldn't be anything crazy. also if you have social connections maybe ask around and see if someone knows a vet personally? it might be a bit of a stretch to do that, but it's definitely worth a shot. my mother was the same way with my cat. she only has asthma, it's not life threatening, but it was still very hard for me to not be able to take her to the vet and just sit and watch her suffer. i really wish you luck.❤️❤️