How to convince my mom to let me buy a hamster?

I really want a hamster. I have a dog and a cat. I take care of the dog myself the cat is my moms. but she thinks it will be to much work which I dint get because I take care of a dog and dogs take a lot more care than a hamster ill use my own money I have a lot more than I need I wanna get one of those maze cages with built in toys and wheels. Do you know where they have the cheapest one how do I get her to let me buy one they r so cute I want one sooooooooooooooooooooooooooo bad