If the scratches are not too deep, I.e. right down to the primer I have (myself) used a black indelible marker pen to touch up scratches. The beauty of this is that you can (with a steady hand and a fine tip) actually touch up each scratch individually. Not the most professional job in the world (I'll grant you) but it's definitely cheap and (in some cases) quite effective.
When you are satisfied that it looks better than it did. Apply some clear lacquer to finish the job off.
Good luck and Si thee