If you want a double-stack 9mm, the SIG SP2022 can easily be found new for $350. I don't have much personal experience with the SP2022, but I've heard only positive things about it.
If you want a single-stack conceal-carry, the Kahr CM9 occasionally goes on sale at Palmetto State Armory for $350. I got my CM9 there for $337 out the door (factoring in sales tax and a 10% store opening sale). The CM9 is a fantastic little pistol - well made with a nice smooth (if long) trigger, uber-reliable (mine didn't need any break-in, ran perfect right out of the box), and surprisingly soft-shooting for such a small and lightweight gun. I would personally rate it much higher than the Ruger LC9, M&P Shield, or Beretta Nano. About the only thing in it's class that I think is a clearly better pistol (not counting the Karh PM9, which is just a more expensive version of the CM9 with a polygonal barrel and a fancier slide) is the Walther PPS, which is much more expensive and a good bit larger.