I think etching my PowerBook is one of the coolest things I've heard in a long while. A simple design, not too complicated or big, would be amazing. My cuurent book falls out of warranty soon at which point I'll probably start tearing it apart, adding new a hard drive, a SuperDrive, and replacing my not-so-professionally scratched lid. Now I'm seriously considering having the new lid etched before I install it. If I'm already gutting my 'Book, I might as well mod the case as well.
$200 seems a little high for a simple etch job, but its a specialty business so its to be expected. If I was a little more daring I'd try to get someone in the machine shop at my University to do it for me for cheap. Honestly though, how often do you just happen upon a laser etching machine?