I'll give my two cents, having converted to premium over a year ago.
While you can find good fit at any price point, and you can find shoddy craftmanship at premium prices, the difference with premium denim is - hands down - the quality of the fabric. Not all premium denim is going to be made of quality fabric- but the chances are lower that you will fine quality fabric at a low price. It's a matter of economics.
Think about suiting. Have you experienced suiting that pills, develops "shine," drapes poorly, and just doesn't feel as good between your fingers and on your skin? Have you experienced suiting that does none of these things and lasts and lasts forever? That difference is the quality of the fabric. You get what you pay for, and better fabrics simply cost more. My dad and my husband have suits starting at $800 that they've had for decades and still look great. I have purchased suiting for under $100 which, although they fit impeccably (always the top priority for me), they pill under the arms and develop shine after a few visits to the dry cleaner.
If you've ever sewn, you also know through experience that it's easier to work with quality fabrics so starting with better fabric can lead to better craftmanship, in the right hands.
So essentially, it's really all about the fabric.
My first premium purchase was COH Huttons, which are made of japanese denim. I have no idea what this means, exactly. All I can tell you is that these trouser cut jeans are as soft as wearing sweat pants and yet they look crisp and sharp and continue to do so wash after wash.
Whatever denim they use for the COH Elson's is just as fantastic: it gets softer which each wash, while still looking sharp. I could sleep in these jeans, and that is saying a lot. It sounds weird, but I like rubbing my hand along the fabric because the tactile experience is just so nice. Having decades of experience with non-premium denim of numerous brands, when I put on the COH, I sometimes think, "This isn't even denim... it's like a class of its own!"
I can't speak to other brands because other than a pair of Earnest Sewns, all my premiums are COH brand.
I will add, however, that my Urban Outfitter cigarette jeans are really nice too. They are so comfy. And they were only $56. I doubt they are premium, and I don't know how they will hold up over the years, but I am liking them very much. So yes, you can find decent jeans at non-premium prices. And I do know you can find crappy jeans at a premium price. I think it's more of a matter of your chances of getting better quality are simply higher with premium jeans.
I'd recommend, even if you premium is not in the budget, trying on premium brands just to get a sense for the difference in the denim. This will make it easier to discern quality in non-premium brands.
