The whole reliability thing often gets blown out of proportion. Of course they will always have exceptions to any rule but the vast majority I would say even from $300-$600 will be reliable guns.
Agreed. I've experienced $179 handguns with thousands of flawless rounds on garbage ammo and $800 handguns that choke up if they don't get a prescription diet in a specific brand of magazine. I've been pleasantly surprised by budget guns, and disappointed by expensive ones. It all just depends.
I think reliability comes down to testing your individual weapon more than making any type of sweeping assumptions about brands. Obviously expensive guns are going to be objectively "better" than cheaper guns -- no sh*t -- but if I can feed several hundred rounds without issue through anything I'll consider that "reliable" enough for my standards.
My working assumption is that anything we see in a retail store from a big brand these days is going to have millions of dollars of R&D behind it and will more likely than not shoot just fine. Modern firearm production is just too good to make broad assumptions beyond what we'd normally expect from the price-to-quality relationship that applies to any product or service on earth.