There is nothing to reverse engineer from Gucci and others. They are mediocre products that get boosted by brand name and white worship. Quality counterfeits (not $1-2 ones) are essentially their carbon copies that you won't be able to distinguish unless you were told from the start. You won't see such situations with the products that actually rely on technology and R&D rather than brand groupthink. For example, Apple has both but you won't ever find a cheap carbon copy of the iPhone - it will have inferior hardware and software, making it a completely different and objectively worse product.
The actual production cost of a luxury bag is around $200-$500 from what I gather
The rest is profit and marketing costs for a "luxury" product
Last year, Alexander Wang sent a model down the runway at New York Fashion Week in a leather biker jacket that cost $2,995. A startup called Italic found the same factory that Wang used and created a similar jacket—including the placement of studs, zippers, and a belted waist—that was distinct enough that it wasn’t considered cribbing the design. Italic’s price? $280.