Kind of a cross between what @Fiddle_Playing_Creole_Bastard and what @janbb said—figure out how much you need to save each week to get the PS3 in a timely matter. Then, figure out how much you need to cut out of each of your areas of spending—food, gas (if possible), clothes, things, gifts, etc.
Every time you’re about to spend money on something, ask yourself if you really want to. Or would you rather have that money available for some other use. If you really need what you’re about to get.
...Maybe have a small picture of the PS3 in your wallet, so every time you’re opening it up, you see it. haha : ) Within sight, in the mind.
Compare items—a lot of things are the same product for different prices depending on the brand name.
Just overall, try to become more conscious of where your money is being spent. This won’t help just to get a PS3, but to develop saving habits for the long run.