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I collect denim jeans. I have roughly 150 pairs from dozens of manufactueres many of them are premium brands.

Generally American, Italian, Japanese and Hong Kong made are the best quality. Japanese denim is considered to be the best quality material as they back in the 1960's bought America's used denim looms when American mills bought new looms. Thus the Japanese are making vintage quality denim and that is one reason why American vintage denim jeans are so pricey.

Pricing on jeans can be a very modest $15 to 250k but those are couture encrusted with precious stones. Generally just over a $1000 is the upper end. Quality does cost as good material, fit and finish adds cost.
Here one thing to note is that the better brands use Selvedge material in their construction

Some of the top brands i am familar with. are the Japanese Evisu, RMC, PRPS, Zegna, Diesel, Armani, Burberry, Ralph Lauren, True Religion, 7 into Mankind, Citizens for Humanity, Affliction, Boss, Riv de Cru, American made Lucky, Antik, Mek..

Some other brands that I like are Buffalo, PEPE, Coogi, Girbaud, Laguna Beach, Angelino, Artful Dodger, LRG, Quick Silver, Carhartt, Daniel Crieumex, American made vtg Levi, Black Label, Joes.