Name brand guitars that sell for much less than their flagship models have two thingns going for them that keep the price low: cheaper labour costs, and autmated production techniques.
Now, the folks who produced the very best golden-age instruments or their components (e.g., the legendary Abigail Ybarra at Fender) were not Ph.D.s in acoustic physics. They were regular folks doing regular jobs in factories who learned on the job and became accustomed to the things to watch out for and how to avoid problems. Which means that folks in Korea and other places can just as easily learn how to make things too. Indeed, we forget what a rich tradition of fine craftsmanship exists in those Asian nations that also make guitars, whether we're talking wood, jade, ceramics, or other materials. There are no barriers to people working in a Fender, Samick, Ibanez or other plant learning how to do it right.
The demand for instruments that makes it reasonable to relocate business to Asian countries also makes it imperative to use automated methods to produce them. Obviously, there are humans in the mix, but the working assumption is that if you can produce necks using CNC methods, do so. Are these methods capable of producing good instruments? Sure. Heck, there are many reasons to assume that a CNC method can reproduce a neck of a certain profile with greater accuracy and reliability than a craftsman could.
Where the two approaches differ is in keeping an eye open for the details. So the glue joint on a budget instrument might be decent enough, but the same glue joint on the high end might entail some addition prepping of the surface to assure better adhesion and a better joint. One can automate fret installation, but doing it by eye and feel might result in frets being installed all the way along the fingerboard,and having both ends of every fret smooth to the touch, dressed, crowned, and polished flawlessly.
To whit, I recently bought a "budget" Parker. Got a great price on it at Steve's, some 30% less than what the big American on-line places were selling it for. It's a decent guitar that plays well....BUT...the pickups are not particularly good, and two of the frets need levelling (there is a buzzing at the 2nd and 3rd fret for the E and A strings). I'm sure whoever made it did their job correctly, but they were producing it to a mechanical standard, and not to a playing standard. High-priced instruments are made to a playing standard. Someone feels the neck and determines that this is too rough to the touch, or the action can't be comfortably low without entailing buzz. And so on.
A pair of Duncans or a set of Sperzels are obviously going to be the same on a budget as on a high-priced guitar, but someone is going to take the time with a higher-priced model to set everything up right and make sure it works as intended and expected. As such, where one might be foolish to buy a budget instrument sight unseen, one can generally feel somewhat assured in buying a higher-priced model on-line that what arrives in the mail will meet expectations.
Of course, introducing the human element also means that their judgment about playability should be congruent with your judgment, and that may not always be the case.
Consequently, one may make the following generalization about budget instruments, compared to higher-priced ones: The odds are greater that each unit if a higher-priced model will be equally playable, even if idiosyncratic in some way. In contrast, with budget models, sometimes you can get lucky but sometimes not. So, what you pay for is really the sort of attention to detail that results in consistency of product. If the gap in price between a budget and higher-end model is wide enough, and the issues not too terrible, the gap in quality can often be addressed by dropping a bit of money on post-production detailing. For instance, neck and fretboard setup. Or even better pickups and their installation.
