Why does this always have to happen!!?

I've needed a new laptop for about a year now, but whenever my mom has the chance to buy it for me, something comes up. Theres always some bill or something we need that gets in the way. It also doesn't help that my mom is single and a teacher in NJ ( Chris Christie thinks teachers get paid too much! >:( ). It's obviously not her fault, but I've had this laptop paid off for a few months and I need my own laptop for digital art and for school and my mom needs hers for her lesson plans and grading papers, so its very hard to share one. How can we resolve this problem?