We're broke, she can't afford it. I'd REALLY buy it if I could.
Well, have you got any neighbours with gardens that could do with mowing, perchance? I'm sure you could do some chores for neighbours for a little bit of extra money. You could do anything for some neighbours for a bit of money. Cutting grass, washing a car, taking a dog for a walk, watering plants, etc.....
None of it will cost you anything and you may just make a couple of dollars or too.
That or if you have any extra games or toys or things that you don't need/want any more, I'm sure you could sell them to some friends or neighbours. Of course, don't go around trying to flog your games to people, but you could mention it in there.
I'm sure your mother would be nice enough to let you get a game with your own money, especially since it's a cheap game and isn't actually 'bad' in any way shape or form. Ignoring the indecency of the community at times, though. :P