The Kahr PM9 is a lot smaller than anything else mentioned here. You'd really have to step up to a $1200 Rorbaugh R9 to get a smaller 9mm than the PM9.
You can probably get a used PM9 for about $700ish.
Here's a PM9 next to a tiny Ruger LCP .380 and a J frame .38spl:
Any of the other pistols mentioned in this thread are significantly larger guns.
Here's another good comparison pic:
If you've got the money for one, they're the best available at this time, bar none. Very high quality, extremely compact, polygonal walther match grade barrel, and super lightweight.