Springfield GI 45 is a damn fine gun that is really cheap. Springfield Mil-Spec is a bit more, but has just a few more features that are well worth the money.
I carry one of these every day, and I have not ever been disappointed by this firearm in any way, I even harvested a deer with it this year, 60 yard shot, dropped 'em like a brick.
Stainless - $650
Parkerized - $600
at least those are the prices I found at a glance on gunbroker.
I dont like ruger, the guns have demonstrated tpo me that they work, but when I think of ruger, I think rimfire, not combar handgun, thats just me tho, the reality is they are fine weapons. A lot of this has to do with ruger's poilitical stance, I dont want to be reliying on a factory like ruger for standard capacity magazines, and factory magazines are what you should use. (with the exception of 1911 magazines, there is no 'factory' 1911 magazine except the ones from either world war, theres no blueprint out there with dimensions, you just have to find a brand, a good brand that works and stick with it) and being as this is to be used as a defensive tool, it must utilize standard capacity magazines.
a glock well, it's a glock....and I dont mean that in a complimentary way, theres no reason to rehash this here, some people like em, I dont, decide which one you are and start collecting propaganda to throw at your opponents whenever a glock thread pops up
the XD's are around 450, it's a good gun. Springfield has really put Glock to shame, they've essentially beat them at their own game if you ask me, they've even outdone HK with this one IMO, I'd carry one, but I'm a single action kinda guy, which is why the HK's still appeal to me.
so I say either the XD or a Mil-Spec 1911. I would start off with browning's design, it has endured this long for good reason, and the fucking thing is just so damn classy.
p.s. if it says kimber on the side and has an external extractor, be very wary, ESPECIALLY if its a used gun.
I dunno if this is really gonna matter tho as they are a little out of your price range.
post post script: also, if you get a 1911, you can get a .22 slide, and shoot shoot shoot shoot shoot shoot shoot shoot shoot, you get the idea...
depending in your familiarity with firearms you should prolly start with a rimfire anyways.