as far as my limit on price i'm looking around $400 - $600
Go Glock! You won't be disappointed. They are without a doubt the perfectly designed personal defense autoloader. They are also right within your price range - and you might be able to find a nice used one for under $400 if you look hard enough.
I bought a used model 17 for $250 a few years back. It was an older model and the finish on the slide was well worn, but the barrel and everything else about the gun was functionally flawless (Glocks will take a lickin and keep on tickin). About a year ago I sent it back to the factory and had the slide and barrel refinished (Cost about $60) and now it looks as good as it shoots.
Their sub-compact models are great for concealed carry - perfect size, lightweight, easy to conceal and they bring plenty of firepower to the fight. Above all, they are reliable as all get out. There is a lot of piece of mind when you know that your gun will go bang each and every time you need it to.
P.S. Another thing I love about Glocks is that their subcompacts will also take their full size pistol magazines. So I can use a 17 rd or even a 33 rd mag in my subcompact 26 if I ever had too. 33rds of 9mm make a pretty nice little home defense weapon and then it can easily transition into a carry gun with the 10 rd model 26 mag.