I got to say, my S&W Sigma in 9mm goes bang every time I pull the trigger. I carry it always. It was my first purchase and have gone up the ladder with additional pistols. Ruger, Beretta & Sig.
My Stoeger Cougar in 9mm is also a good choice for a cheaper pistol.
A realistic picture of the cost of ownership might help your friend out. Frankly, $500 on a handgun isn't the largest component when you start thinking in terms of spare mags, cleaning/maint tools/supplies, cases, holsters, ammunition, responsible/safe storage, and training over a lifetime of ownership. Add that all up. A couple thousand rounds of 9mm can cost more than $500 by itself.
Does going cheap on a piece of life-saving equipment, i.e. a handgun, considering the whole scheme of things, make cents (see what I did there?)?
Be that as it may, if $500 is the cutoff, then here are some options (in no order):
This. I'd take some time to find a good used gun. As others have stated, you need to consider availability of holsters, and mags and the price of those items as well.
I bought a Charter Arms Off Duty about 6 months ago, it's gone bang every time I have pulled the trigger and for the $250.00 (new in box) I paid for it I have no complaints, lifetime warranty also. If they stay in business.
My son and I collect firearms, so have some Colts (Way above the $500 mark), Ruger's, Remington's, Springfield's and several Military handguns, as well as RIA (real inexpensive 1911 - great value) as well as a few Bersa, Jennings, even some Cobra Derringers. Honestly other than the appearance of the cheaper firearms (fit and finish) none have really shown to be unreliable. We haven't fired many rounds thought the Bersa or Jennings (probably 2 ~ 3 hundred) but haven't seen any failure to feed, fire or eject.
We do inspect and "tweak" any issues before shooting ~ if heavy machine marks exist on the feed ramps I will remove them, and all burrs on the firearm and mag feed lips, are stoned off, possibly that is why we have no issues.
As far as a inexpensive firearm to carry, if a 1911 is your preference, I don't think you can go wrong with a RIA, for about $350 new, don't think you can find a more reliable firearm for less than $1,000. Actually I would feel pretty secure carrying any firearm we own!
I'll say a S&W SD40VE. I had one, the trigger is long and heavy, but it went bang everytime I pulled it, of course if the cut off is $500, I'll go with my M&P .45, everyday low price of $499 at Plainfield shooting supplies
Are higher quality used guns acceptable? I though we were going under the assumption that the better made guns were not available? If we can include any used gun under $500, I'll go with the 70 series Govt. model in brushed nickel I just picked up. I paid $600, but after selling off all of the WC extras that came with it but were never installed, I expect my actual to be well under$500.
[Sorry guys, just had to brag on this one.] [Oh, almost forgot, it looks like new and when I put back the original sights it will be all original]. [Had to say that too]