I find most newcomers dont understand it mostly because of blissful ignorance
Higher end boards have a ton more features. They offer better/more mounting styles, leading to either a better sound (Top mount) or better feel (gasket mount) as compared to the tray mount which leads to a very stiff typing experience with inconsistent sound
They also are made using more expensive materials. The most common would be CNC aluminum, usually also with a Stainless steel/Brass weight. All adding to the cost as well as making the board sound good. Weights can help make the board sound more full, and not flat. Bottom weights also make the board look good
Annodisation and e-coating also cost more than just painting plastic
You also get much more options in terms of PCB and Plate. This affects the sound and feel of the board. Want better sound? Get a 1.6mm non flex cut PCB. Want most flex? Get a 1.2mm flex cut PCB. Want a deeper sound? POM/PC/PP/Brass plate. Want a clackier sound? FR4. Want a neutral sound? Aluminum
Then there are more minor things with these PCB/Plates. Such as more layout support (split backspace, split spacebar, stepped caps lock etc.), support for PCB mounted stabs (generally considered better than plate mount) and south facing switches (for better compatibility with cherry profile keycaps)
A 20 dollar barebones kit would not be the same at all as even a 100 dollar enthusiast board.
Imo most of the “Cheaper” options are literally just boards targetting most of the newbies or wannabe custom keyboard people, and is literally just you assembling something like a razer keyboard…which defeats almost the entire purpose of building custom…
With keycaps those you find in stock tend to be more expensive because most were sold through group buys. That essentially means that there is a period of time where orders were accepted, and after that orders are closed and production begins. Once production ends there is no guarantee the product would ever come back to market, creating a limited quantity and jacking up the price of extras. Not to mention that the fulfillment date can sometimes be up to 2 years after orders were closed, so vendors can charge extra for the long wait time
As for what they offer, usually they are made with thicker plastics, have MUCH better QC, offer more in terms of novelties, offer more in terms of different layouts (Tsangan, WKL, Stepped caps, split spacebar, split backspace, F13, 1.75u shift for 65/75%), more unique fonts, more secondary fonts (hiragana is the most common, some sets like shanshui or norse have secondary fonts in other languages such as chinese)
As for main difference vs clones the thicker plastic and better QC is the main thing, as well as the feeling of buying authentic rather than fake. But the QC imo is the main thing. Some clones i’ve seen have had really goofy fonts. Stuff like “Shift” becoming “Shitt” isnt uncommon, pretty sure i had a “Shift” become “Shiπ” and another that was “SHft”. Its most easily seen on the shift/enter keys but can happen to other keys as well
All in all you need to come in expecting to have to pay for a superior product. Else you are just gonna assemble literally the same thing you were gonna buy but at a higher cost.
It’d be like wanting to get into coffee, realising all the coffee beans and machines cost too much. So instead of just taking the plunge in, you just buy instant 3 in 1 coffee and ask everyone “why does the coffee hobby cost so much when instant coffee is so cheap?”, totally ignoring the whole point of making your own coffee.
You arent finding the cheapest path to the goal. You are trying to find the best goal
Razer mice, stuff from Pulsar, Lamzu etc.
Finalmouse too, but thats a different price category and not exactly easy to get right now