There is absolutely no doubt that branded goods carry the brand premium, which is the price a buyer is willing to pay over and above the price that a similar unbranded product. It is the cost of the prestige associated with saying "This is Burberry".
In my experience with clothing, the brand premium on the MSRP over the cost ranges from 300% to a whopping 5,000% of cost.
On accessories, these go even higher.
The difference is the material and the finish. A good brand would always carry a high quality product and would pay a small premium to the manufacturer so that the quality is up to the mark.
Cheaper cashmere products have become hugely popular recently. These claim to offer the quality of cashmere for a lower price, some may use a slightly lower grade of cashmere, or different processing methods to make the end result more affordable. And while they are comparatively cheap, they're still usually at least twice the price of wool.
There have been extreme cases of mislabeling too, and some supposedly 100% cashmere products have been found to contain yak hair or even rat fur. If you do find a really cheap product that claims to be cashmere, it may be too good to be true.