How can I convince my parents to let me get a horse?

Hi, I've been riding horses since I was 10 and I absolutely love them. I've asked my parents if I could get a horse, but they keep saying no because my mom's friend's horse developed really bad colic and she keeps telling my mom about the vet bills from that. I think that my parents should get an opinion from more than one horse owner before giving a definite no. I work really hard and do most of the chores in my family, and ume much of the responsibility for my dog. I have shown that I am really committed to the work piece of owning a horse, seeing as I have worked at the barn for the past few summers, and I will be spending next summer braiding at shows. I know that horses cost a lot, and I am willing to help pay for everything. My mom really isn't a horse person, and I think that's what's holding her back, but my dad seems to really like them. I think it's just a fear of astronomical vet bills that's scaring them off. What should I do?