I don't have any comparison pics/proof or anything but I do have an experience to share.
Awhile back I bought jeans from UO for around $70 I believe. I really liked the fit and color at the time but after a few washes and wears they really lost their color and style and are actually pretty thin quality. They're fun to wear now cause they're kinda cute and comfy but other than that they lack the style they once had and I typically don't wear them out.
They kinda remind me of the quality of $30 pants.
On the other hand, I bought a pair of $60 levis and they are AMAZING. The color is much richer, the fabric is incredibly thicker, and the fit has stayed true despite my many wears.
I guess what I'm comparing here is brand name quality compared to a lesser known brand. Additionally, in this case, the less expensive jeans turned out to be a lot better quality. Although I have seen levis go for about $100+ online, so maybe I just got lucky with my payment of $60. Also they were most likely vintage and some people say stuff was made better/to last back then so who knows.