How can I convince my mom to let me get a violin?

So.. I have been wanting to play the violin for a long long time. I told my mom and whenever I try to talk abut it she always finds away to avoid the question and find a new topic. I live with just my mom and my brother. I am normally patient with things but I just cant seem to wait to get one. I have went on kijiji and found one that is 99.00 and I told my mom I could pay for it. She didnt even really care, I have found a website that teaches you how to play it for free... I rreeeaalllyyy want to play it and I need help to convince my mom!