I have been spending several lunches per week at at Eleven Cafe, 29 Le Anh Xuan in District 1 (Opposite of the New World Hotel). The coffee and food is really good there and the prices very good. I always spend below 100,000 VND here. At lunchtime you need to come about 10 minutes before noon or you will have trouble getting a table.
The atmosphere is really good and relaxing here. My only complaints are the intermittent WiFi and the smoking. I would say about 80% there are patrons that just chain smoke. You cannot escape it and this is one of the main reasons I decided not to visit this restaurant again during lunchtime (this is one of the few restaurants where I have to through my clothes in the hamper when I return home). Outside of that time, there are less people which means less smoke.
I plan to speak to the owner to see if they can make at least the upstairs a non-smoking area. Anyway, it is the law but since this is Vietnam….