Seeking hotel accommodation in suburbs/areas of Vietnam

I am attending a conference (as a professional photographer) in Singapore, during October and afterwards will be travelling to Vietnam spending a week in each of the following city/areas: Ho Chi Minh City, Da Nang & Hanoi (total of 3 weeks).
I have booked flights and want to pre-book inexpensive hotels in the above for the first 2 days during each of my weeks stay and will then book further accommodation once I know where & what I want to go/do/travel/see etc.
When travelling I generally try to avoid tourist areas/sites and I am particularly interested in photographing local life - people just getting on with their lives, ‘street photography’. So the first place I visit in a village/town/city would be the market/local areas.
I would therefore appreciate any advice/recommendations as to what specific areas (central/accessible/interesting/cultural) in Ho Chi Minh City, Da Nang & Hanoi I should look for hotels in.
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