“At the time [the 1920s], pulp magazines were a thriving industry, providing cheap entertainment for millions of readers and employment for hundreds of writers who churned out piece-work at the rate of a penny or two per word.”

– from “The hard-boiled novel” by Sean McCann, in The Cambridge Companion to American Crime Fiction edited by Catherine Ross Nickerson

Adjusted for inflation from 1920 to 2013, that would be 11 to 23 cents per word.