How to convice my mom to let me get faster internet?

i want to play xboxlive soo bad but,sadly,we have Earthlink dial-up speed 56kps and for xbox live to work you need at leat 1mpb dial-up that we use is about 13$ and i found a 1mpb charter deal for 25$ a month,but i asked my mom and she said no she said that we only need the computer for homework and things like that i do homwork on the computer on wensdays and my almost a senior brother might need to use it more. and i could realy like playing xbox live instead of sitting at home all day on saturdays how can i convince her? p.s. she thinks 25$ a month is alot of money?!