How do i convince my parents to let me have a hamster.?

I'ved owned a rabbit before, who lived 4 years and i loved him soo much, and lately i feel like i want to adopt another rabbit, or hamster. My mum continues to say no, i told her i will pay for everything, seeing as my birthday is in 13 days and when i get birthday money i will buy a cage and everything and use my pocket money for food, and treats. I do own a cat, but she stays out my room, and doesnt really bother with me unless she wants food or water. when i owned the rabbit, my cat would always sit by it and sleep ontop of the hutch. i think a hamster would be more of a tempting snack though..my mum is being very stubborn and i don't know how i can convince her, i think she's made her mind. but im not going to give up! it took me a year to the the rabbit so im sure i can wait :)