First rule of manufacturing: you can't make something as cheap as China, period.
Second rule: if you're making less than one million pieces, you can't make something as cheap as 10 times China, period.
Well, that may be exaggerating the difference, but suffice it to say, the cost-per-piece advantage in significant quantities (well over 100) is huge. If you pay a designer to create the product, that NRE also amortizes poorly into that quantity (a small project might cost $5k NRE, so accounts for $50/piece, regardless of production costs).
So, if we instead gear this towards hobbyists, where there's just a schematic to follow on the breadboard, and you wind your own transformer... okay, a lot of those parts can be found or purchased for relatively little. You can buy transformer bits for relatively cheap. Or you can attempt to salvage and rewind them. But with amateur build quality, it might not even work as well as the Chinese thing, and that's after significant time for the average hacker to figure out how the circuit works, fixing his mistakes, and not routing the power and ground signals very well.
I like to make circuits like these, from time to time:
but as far as I'm aware, no one else has ventured to build them. (The main premise is a discrete circuit which performs better than the UC3842 in some respects, though lacking in others. The good old 3842 circuit is of course easy to build as well.)
As with all switchers, getting quiet operation out of these requires careful wiring and extra filtering. Not something that can be done on breadboard (functionally, yes: I developed these on the breadboard, with a little care; but not for low noise purposes, no).
I could make PCBs for some of these, but as I have no particular need, I tend to make deadbug one-offs of slightly customized variations. PCB also forces a very rigid limitation on the transformer: pin spacing, THT or SMT, etc. You're probably as well off purchasing a dev kit for your favorite controller-in-one chip instead.
Tim