Affordable housing in Prospect Heights, ad in the Brooklyn Eagle, October 1916. Note those rents are ANNUAL amounts.
So, a one-bedroom apartment on Underhill and St. John rents for $30 a month (about $712 in 2016 dollars).
Present rates in the building are 1 BR: $2,375. 203 - 209 Underhill
The three-bedroom, two bath apartments on Sterling and Butler rent for $75 a month (about $1,663 today's dollars, but I am too lazy to pull up a recent listing).