Under $300 you will be limited.
Used is your best bet, but this is a bad time to try and find something. There are a few revolvers available for that price and you may be able to find a Smith & Wesson Model 10 used for that budget. It's a good starter handgun.
If you're looking more for training than defense, a .22 might be a good choice as well. The Browning Buckmark, Ruger 22/45, Beretta Neos, and Ruger SR22 are all good .22 autos.
I wouldn't recommend a Hi-Point unless you're just broke. I think they have an unfair reputation, but my main gripe is they are just too unusual for a semi-auto. The manual of arms will not lend itself well to other handguns. Then again, some of my above recommendations for a .22 will have a similar problem.
For a little more, Taurus makes some decent handguns that I can usually get at Academy for about $350. They make a decent semi-auto but I have heard a lot of bad reports with the .45 versions so you may want to keep it to 9mm and .40 S&W. I recommend 9mm for newbies anyway.