Hang Gai is a long strip dotted with shops where you can buy (obviously) souvenirs and as its name implies, "Street of Hemp", silk. A silk dress or robe averages to USD50.00 where USD1.00 = 20,000 VND. Sometimes, much, much more which is the very reason, tempted as I was, why I didn't buy one but instead splurged on souvenirs.
My favorite souvenir shop, Mai Trang, is run by an old lady who doesn't force you to buy anything. In fact, she just sits on her place reading while you browse and will only look up if you need to ask something. This interactions suits me perfectly because I don't fancy being needled into buying. I bought around 40 pieces of bookmarks from her. These are made out of hand-painted bamboo. It's price is 20,000 VND apiece but she gave me a generous discount by giving me four out of 40 for free. :)
I was also able to buy refrigerator magnets which bear landmarks of "Hanoi", "Ha Long Bay", and "Vietnam" for the same price as the bookmarks each. Since I purchased around 20, she gave me two out of 20 for free. I really like her. If you're planning to hoard on souvenirs, Mai Trang is the place to do it. I'm attaching three photos so you can see the address and the silhouette of the lady seller. :)
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.