What do you define as "quality"? Is a heavier frame with a simple layup lower quality than a lighter frame with more complex layup and compliance designed in? The first is probably cheaper to produce but could easily be a more solid and reliable choice. Or are you concerned with how well the frame is finished?
I don't know that there will be a very strong correlation between whatever is used to define "quality" and price. Since there isn't a very good way for us to determine the quality before buying, a lot of it relies on our perception of quality, and that is much less accurate.
I think most vendors are ultimately charging as much as they think they can get, and this might not have much to do with the end experience for the purchaser.
Not to say that there aren't quality differences between those vendors (and even between frames for each vendor) but I don't think there's any better way to determine that than by reading through the posts here and attempting to account for how popular each frame is.
For me it's the latter example. You want lateral stiffness for efficient power transfer, but you also want vertical compliance for comfort and handling. Yes, you can get a very stiff bike that's more reliable, but you get to a point where it's so stiff you might as well get an alloy frame.
Quality of materials contributes to this factor. The grade of carbon (in the right places) and the quality of the resin, will affect weight and provide a better balance between lateral stiffness and vertical compliance.
Quality of workmanship too. If the carbon layers are not laid well, regardless of the quality of carbon and resin, the benefits of the more expensive materials get diluted.
In terms of the finish, yes, aesthetics matter, but it's probably bottom of the list for me.
I honestly have been reading the threads. They have been very helpful, and expect that when I eventually settle on a choice, they will be even more helpful in the build process. However, they haven't answered this question for me, so I was curious as to the views of others on this.
To be honest, just when I think I've arrived at a choice, something throws a spanner in the works. An example: The ICAN A9 ticks a lot of boxes and the A9 thread on this forum suggests most people seem happy with it. The ICAN website also shows that it is a UCI approved frame. However, I've checked the latest UCI approved frames list and I can't see it there under ICAN or Triaero. It could therefore be that this is untrue or it could be that it is true but there is some delay in it being added to the list. There is also one person whose fork had an extra hole in it that had been filled. On querying they were told by ICAN this was normal. There is also a road.cc review that gives a set of ICAN wheels a 3/10 largely due to flex, which makes me wonder about their frames. Even though I've used ICAN as an example, when I research other frames, the issues might be different but the pattern is the same in terms of conflicting signals.
