In 1920, the average wage across all industries in the US was $1407 per year. The average wage for state and local government workers was $1164 per year. The average wage for public school teachers was $970 per year.

http://usa.usembassy.de/etexts/his/e_prices1.htm

So, one person on $100/month, $1200 per year, (not sure if this is income, or post tax spending money?) would have been able to live fairly well.

Just one person, no car, no dependents.

This probably isn't entirely what you're looking for, but George Antheil was a somewhat notable modernist composer in the early 20th Century. Throughout the 10's and 20's he lived in various European cities in various housing situations. At one point in his autobiography The Bad Boy of Music (the name he gave himself), he explains how he lived above the famous Shakespeare and Company bookshop in Paris while living on a small stipend from his patron and self-funding most of his own tours and concerts.

I don't have either of his autobiography or his biography anymore, and his wiki page seems kinda off, so I don't have an exact amount to what he made per month. But as his patron tried to stop sending support many times over their 20 year relationship, I can't expect it to be more than $100

Hope this helps.