Sweet didn't know they still sell them, I might get one.
But when buying batteries you normally want to buy it from 1st party and not 3rd, they just work better. some cheap 3rd party sucks with bad battery life, bad quality control and what not. Battery is another thing you do not want to cheap out but if you do buy from one with a name.
I think that 30$ battery is actually for PSP 1000, so it is bigger, but includes covers for psp 2000/3000. So there is more of a bulge, but not too much and should give you double play time on the 2000.
Edit: I think it is.. but I though they used to be bigger capacity but I guess not.