Welcome to THR!
I admire you for taking the courage to invest in yours and your families safety. It is a WISE decision.
I grew up very poor and have experienced hard financial times before. I know the value of a dollar. My advice with buying a gun is to buy one good gun rather than a few crappy guns. And the difference in price between a good gun and a crappy gun really isn't that much money in the long run (the life of the gun, even over just a few years of shooting enjoyment and gun reliability). You could arm yourself incredibly well if you shop the classified adds and buy one from a seller face to face. I would not buy the Nagant pistol for my primary use pistol. It's a great novelty, but for real self defense there are much better options.
You can get great deals face to face with sellers if you know what you're looking for. I've bought several fantastic handguns for $300 each. You just have to do your homework, save your money (skip some luxuries), and be ready to pounce with cash in hand when you see a deal. A few dollars more and the quality really jumps in the $300 range.
If you keep your eyes open, you should be able to find a Ruger or S&W 3" revolver in the $300 range, or a CZ, Glock or Ruger 9mm in that same range. Another great bargain now is the CZ82 in 9x18 for $220! The lesson is to spend just a bit more than your initial price point and you'll get a significantly better and more reliable and enjoyable handgun. Since you're on a budget, the best guns will be ones that fire the least expensive ammo, like the 9mm. It is perfectly acceptable as a self defense round, and you can afford to practice. One mistake people make is failing to practice practice practice.
Good luck!