The OP has lived here 20 yrs but lives in Chiang Mai which is notably less expensive than Bangkok. He was just trying to help his Thai citizen daughter move since she graduated from College earlier this year.
First, His daughter is a Thai citizen. You assumed she was an expat too?
But if a foreigner wants or needs to live cheaply, let them live as they want. Even someone spending less than the average expat is bringing money into Thailand that is being spent which helps businesses depending on their business to be more successful.
For all the people making snarky comments about how low the price is, have you never thought about who lives in these often older buildings often with no name that seem to be apartments? Have you never talked with poorer thais about where they live and how much they pay? I was talking with a security guard at my old place and I was talking about places I was looking at to move to. The rent price was 20k and he said that was more than his entire month salary, Let that sink in. A full time Security guard was making 20k or less a month.
Here's a 42SQ M @6000 Baht place in that area
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Someone mentioned RentHub. There are a LOT of cheap serviced apartments on there. I think with Renthub they essentially expect you to find them on there and then make a physical visit.
If she goes south of the River there, it gets quite a bit cheaper quickly. Not much cheaper than the above link but more choices and slightly cheaper.