That's physics, and no amount of "quality" in the manufacture of the firearm will fix that.
Indeed. Manufacturing quality isn't magic. Anything will deteriorate when subject to the right conditions.
As to the original question - in general, I abhor the outdated "you get what you pay for" phrase. The reason being is that for manufactured goods, it's vaguely accurate at best. It attempts to set a strict ratio of cost to quality, which just doesn't exist. Sure, a $100 pistol probably will probably not work as well as a $1000 one, but there are many $400 pistols out there that work just as good as $700 ones. A lot of times mere name brand recognition causes a value to change merely based on perception - not quality.
That aside though, were are increasingly moving into a digital era where many of the things we use don't really exist in the real world. Computer software for example. You can make a physical disk to hold it, but the value in software is not in the $0.10 disc it shipped on. It's a digital pattern. I've heard the "you get what you paid for" mantra applied to software where it absolutely doesn't apply. Software cost will vary by the number of perspective buyers, and by the level of compensation desired by the programmer (some programmers write software for free just because they like to, and much of it is of very high quality). Also, Microsoft can sell Office for a few hundred dollars because they have millions of buyers. A company who makes a pretty bad, buggy piece of software meant to process veterans benefits claims might charge $100,000 for their software in comparison, when it's obviously of lower quality, merely because there is a demand, but only from a very limited number of customers.
When combined with similar situations is it applies to digital music, movies, etc, "You get what you pay for" is quickly going the way of "the world is flat".