Some progressives blame high housing costs on inequality. But in the 1920s, inequality was as significant as it is today, if not more so. However, there was apparently much more low-end housing, according to a book I just read, Living Downtown: The History Of Residential Hotels In The United States, by Paul Groth (which I recommend to everyone interested in these kind of issues). Groth focuses on residential hotels; until the growth of zoning, hotels and apartments were interchangeable.
The difference between the 1920s and today is the following: today, the only multifamily housing options available to most people are
By contrast, in the 1920s, there was a wide range of housing between #1 and #2, and even options between #2 and #3 as well. For example, today an apartment typically has a private kitchen/bath/etc. In 1920, that was an option for the middle and upper classes. For the working classes, you could share a house with a family, or live in a residential hotel with shared baths, some with a kitchen, some without (the latter presumably cheaper). If you were poorer, you could live in a cheaper hotel with cubicles. If you were poorer still you could sleep on a floor, and at the very bottom of the market, you could sleep in a movie theater at night.
How cheap were these low-end alternatives? Groth calculates that in San Francisco, the lower-middle classes could live in a rooming house with a bath down the hall for $4-10 per week ($50-140 today, or $200-600 per month). A cheaper, nastier version of the same was $3-5 per week ($40-60, or $160-240 per month).
A cubicle was a quarter a night ($3 or 4 today), or $1-3 per week ($60-160 per month). At the very bottom was a true flophouse: 5 or 10 cents a night (a dollar or so today) for a dry space on an open floor, still better than sleeping on the street.
Now of course, all this affordability had a cost: much of it was not "decent" by today's middle class standards. It seems to me that you can have regulation-induced decency, affordability, or a low cost to the public fisc. But you can't have all three.