350-400...Hmm I would say to stay with 9mm Nato caliber for lower ammo cost.
As to the actual gun. You would be looking at used mostly in the price point you mention, with the exception of Bersa and Taurus I believe. I havent had any recent experience with their products so I cant comment.
As far as used, I would say look for something like a S&W 5906, or a Beretta 92, an FM Hi-Power, Ruger P series, should also be some used Glock 17 and 19's around that price. You may be able to find a Rock Island 1911 in 9mm for that price very lightly used as well.
As far as surplus, you should be able to find several in 9x18 mak caliber, mostly of eastern european design. I havent checked want century arms, and southern ohio guns has in stock, but you may want to check there. steel case 9x18 is pretty cheap as well, though not common in some areas of the country.
Any idea on what type of handgun you would prefer or want? Your best bet for something concealable would be something from the surplus market or maybe a Bersa in that price range.
Hope that helps, give some more specifics and maybe some of us can help you narrow things down