Snakes, all I can do is ask why you aren't already prepared to defend yourself properly? Didn't think about it 'till now, did you? Guess what? You should have! It is called planning ahead! You had enough warning and ignored it.
Seriously man, self-defense is a human right protected by the Constitution and a duty of all responsible people. Whether it is martial arts, baseball bats, or guns, it is your responsibility to defend your own life and safety and property and not that of the police or your landlord.
Thugs like your neighbor are cowards who prey on the typical spineless sheep. Stand up to them with overwhelming force and they can't run away fast enough.
I can tell you from personal experience that in the nearly 16 years I've carried a gun for self-defense that it has made a difference in my favor more than once, protecting both my own personal safety and also my property. Thankfully I've only had to draw it a few times and never had to pull the trigger, but had I not had it in my hand things would have turned out far worse.
Guns in the hands of law-abiding citizens are the most powerful deterrent to thugs like your neighbor, more powerful than the police.
If you've got $600 to spend, go get a license, take classes at your local range, and then buy a handgun. I carry a Springfield Armory XD daily (.45acp 5" Tactical). XD: $550. License: $40. Holster (Blackhawk SERPA): $30. Time at the range: well that can get expensive but is well worth it. At the range, you learn to shoot properly which gives you a distinct advantage over the thugs who like to hold their guns sideways because it looks cool and that's how their role model gangsta rappers do it.
Far as your company's rules go, screw them! Your life is worth more than their rules. They can not garantee your safety, only you can do that. I've carried on every job I've had since I was legally able to at 21, including Domino's Pizza. Worst they could do was fire me (which none ever did, in fact I used to "ride along" with other drivers into bad areas before we just cut them off) but the worst the thugs could do was kill me. I made the choice.
You've got a killer deal on rent, but the reason rent is so cheap is because of the area where you live. And it is only going to get worse, so yeah you're gonna have to move eventually. Sooner rather than later. In the meantime though, you have immediate safety concerns that must be addressed and the responsibility is yours and yours alone.