Postcards in Hanoi are really really cheap. You can buy 10pcs for a dollar. I have bought a postcard set of the Old Quarters in Hanoi.
Personal experience in Old Quarters: The place is a time-travel experience. Vietnam in general is like the Philippines, but when I am in the OQ, it feels really Vietnam-ish. My hotel is in the heart of the Old Quarters–the colors, the fragrance, the noise–making my Vietnam trip an unforgettable one.