Have you ever tried the "Falcon" Z-77 keyboard? It's been rebranded/knocked off by several Chinese manufacturers (different brands all have the same distinct falcon logo in the top middle of the keyboard) and is available on Amazon for around $30.
I bought one (the HUO JI version) after encountering several reviews from folks saying it compared favorably with their $100+ boards. I'm quite happy with it, and it's hard to have any idea if I'm missing out on anything and, if so, what I'm missing out on.
There are different shaped keycaps, like different profiles. I don't really understand that yet, I have some made specifically for an ergodox style layout, so they probably have slight differences.
I'll give a few recommendations, cheap and expensive.
First thing you should know is most of the expensive sets are abs, but abs eventually gets shiny and PBT does not. The material itself doesn't really dictate the quality beyond that. Some people prefer the naturally more textured feel of PBT and some people love the smoothness of ABS. I can tell my GMK abs keycaps that I spent $170 for are more lovingly crafted than my $30 PBT pudding caps or my other set of white backlit caps that cost around $40, but when typing on them I honestly couldn't say I have a preference.
Some people find no-name chinese sets that are made of good, thick plastic that are almost comparable to more expensive sets. Generally thicker keycaps are better made.
In general though, for the real high end stuff, a company called signature plastics and another one called GMK make most of the sets. They are about $100-200 in group buys. They sell small run sets on a bunch of different websites. The way you buy them is basically keep watching /r/mechanicalkeyboards or /r/mechmarket for a while until there's a group buy for one you like, then you put up money. There are some of these sets readily available on a bunch of different vendor sites, but they change all the time because of the limited nature.
Basically what you are paying for is double-shot abs or whatever other plastic they use, basically there's an inner layer and outer-layer melted together in a way where for the inner color only the character shows through to the top. It makes the keys last pretty much forever without the character wearing off (contrast this with my 2016 alienware where the WASD started wearing off in 2 weeks).
There are cheaper sets that are double shot, but there are less options for color and there's a small difference in the fit and finish. You can get a decent set of backlit keys for about $30. You can get a slightly better set for $40-60, and then there's the $100-200 sets that while, aren't a life changing experience to type on, have more options for how they look and they do have a high level of craftmanship that you can really only notice when you are inspecting the inside/outside of the key before you install it.
Some people obsess about the perfect accuracy and design of the individual characters on the keys, but I don't find that to be a big deal, but the more expensive sets do a better job of this.
As to what you are missing out on? Well, my first kit was a solid aluminum case and I filled it with a layer of some rubbery heavy stuff that I can't recall the name of, but the end result was a keyboard that's like 5-6 LB and it feels absolutely solid and absolutely amazing to type on. It was about $300 with a cheap set of keycaps. My newer more expensive one has a plastic case but I bought it for ergonomic reasons. Plastic cases can be very high quality though (this one is) and feel very good. However, if they made a version of this out of a solid block of aluminum like they do with more traditional keyboards, I would like to get one because there's still a noticeable difference in solidity and quality.
This is one of the cheap sets I liked. Its sold through but it pops up every once in a while, if you don't want to wait I think amazon has an almost identical set that could very well have even been made in the same factory for a different brand:
I encourage you to check out the mechanical keyboards subreddit's sidebar, there's a ton of information for helping people pick stuff out, that's how I got into it.
As a complement to phaus's excellent comment, I'd like to talk a bit about keycap profiles. The two main categories are cylindrical and spherical profiles. Almost all off-the-shelf keyboards have cylindrical profile keycaps on them by default -- essentially, it's as if a cylindrical chunk has been removed from the top of a flat keycap. OEM profile and Cherry profile are the two most common cylindrical profiles (the keycaps that come with most off-the-shelf keyboards are OEM profile). A spherical-profile keycap has more of a fingertip-shaped divot in the top (SA, MT3, DSA, and XDA are the most common spherical profiles). I personally find spherical profiles more comfortable than cylindrical profiles, so you may want to give them a try, but if you're happy with your current keycaps then you're probably not missing much.
The other major factors that describe profiles are height (hi-profile keycaps are taller than low-profile keycaps) and sculpting. With a sculpted profile, the keycaps on the top rows of your keyboard will be tilted towards you, the keycaps in the middle will be flatter, and the keycaps in the bottom row will be tilted away. Many people find this more comfortable than a flat profile (keycaps from any row of the keyboard are shaped the same), but others find flat profiles feel equally nice, and if you're using a layout like Dvorak or Colemak it's easier to switch your keycaps around to match (with a sculpted profile you'd have to buy an entirely separate kit with the alpha keys in the correct location). Hi-profile keycaps will be taller and, if they're sculpted, are generally sculpted more dramatically sculpted than low-profile keycaps. Sculpted keycap shapes are generally described by row number, with Row 0 or 1 used for the F-row and Row 4 or 5 used for the spacebar and modifier key row. (Numbering systems are not standardized, but R3 should always refer to the home row.)
Of the spherical profiles, SA and MT3 are hi-profile and sculpted (except for a few SA sets, which use all-row-3 keycaps and are therefore flat), and DSA and XDA are low-profile and flat. Low-profile sculpted spherical sets are rarer -- MDA profile was recently developed to help fill this niche, but you will have trouble finding an MDA set outside of group buys.
In terms of actual recommendations? Budget-priced spherical sets are unfortunately thin on the ground; they haven't really left the high-end group-buy-only enthusiast market, whereas there's a lot of cheap OEM profile sets with a variety of aesthetics. I own and like the Matt3o Nerd DSA set [1], which is currently in stock and costs $50. (Signature Plastics keeps some DSA sets in stock on pimpmykeyboard.com, but they're all $80-$100.) For a sculpted set, look at Maxkey SA sets on kbdfans.com (also priced at around $100, but it's a slightly better price than Signature Plastics' SA sets).
Have you ever tried the "Falcon" Z-77 keyboard? It's been rebranded/knocked off by several Chinese manufacturers (different brands all have the same distinct falcon logo in the top middle of the keyboard) and is available on Amazon for around $30.
I bought one (the HUO JI version) after encountering several reviews from folks saying it compared favorably with their $100+ boards. I'm quite happy with it, and it's hard to have any idea if I'm missing out on anything and, if so, what I'm missing out on.