Either add a hundred or so, or consider $100 or more of your budget for ammunition. The absolute worst thing you could do is buy a gun, maybe shoot it a few times, then load it and put it away for home defense. You didn't just buy a car, get in, and drive away. As you stated you have absolutely no experience with guns of any
kind. You will need to learn, not just go out and shoot a couple times, but learn
, and practice....A lot!!!
As to suggestions for your purpose, there are many quality handguns in the $500 range from Ruger, Smith & Wesson, Beretta, and more that would fit your needs. I'n not sure I would suggest a Glock for a person completely unfamiliar with firearms. Not a condemnation of Glock, but with the only safety being the safe action trigger it may not be as safe for a complete newbie.
Please, I didn't mention the Glock to start a Glock argument. I like Glock, I have a G20 that is one of my favorite guns. A G17 is on my short wish list because it was the one that started it all, and you can never have too many 9MM's. I just think that for a beginner a mechanical safety on the gun would help lead to better safe gun handling practices.