Upgrade or not

I don't have enough money to get a brand new Mac right now but I'm going back for my masters and need a portable laptop.

Right now I have an iPad 2 and a MacBook pro 2008 2.4ghz 500gb. I can either buy a used air or MacBook pro on craigslist that's newer than what I have, or I can upgrade my pro with a 550gb solid state hard drive, 6gb of ram and a new battery for roughly the same amount.

What would you do? Or would it be another option that I haven't listed? Any and all help would be awesome!

 

$800 is going to be too much for me to handle, classes and books wiped me out.

As far as what I'm going to be doing, I'm going to be doing a lot of finale work (music notation)m other than that it'll be basic computing needs. Right now the computer is very slow, always has to be plugged into an outlet and frustrating to use.
Luckily where I love I can find some cheaper used MacBook pros and airs, but I've also heard that a memory upgrade and a ssd hard drive upgrade can revive an otherwise sluggish computer.