If you can't afford Perma-Spin, tooth paste works as an excellent substitute. Using about enough to cover your index finger tip, get the cd wet and buff it in circular motions. Only do this as a last resort however, as there is a small chance you could damage the CD even worse. I had a music CD that I didn't care about anymore (Ace of Base.....shut up) and it had a huge scratch in it. It was completely unplayable past the first 15 seconds. I used this method, and you can't even tell it was EVER scratched.

If you're curious how I discovered this, it's an old jewler's trick....used for getting scratched out of quartz in timepieces.