These names are references to wages. In chapter 24, Pa uses the term "twenty cent men" when he talks about how a man came to the Weedpatch camp looking for workers. Pa tells us that the man said he had already hired some "two-bit men" (meaning men who would work for twenty-five cents an hour) and were looking for men who would work for twenty cents an hour. The man identified in the story as "Black Hat" said that is how the wage keeps dropping - the employers offer lower wages than currently being paid because the people need the jobs so desperately, they will work for any wage. If an employer says he has work for twenty people and he'll pay twenty-five cents, he'll get just as many workers if he offers to pay twenty or fifteen cents because any wage is better than no wage. So, a "twenty-five cent man" is one who will work for twenty-five cents an hour, a "twenty cent man" will work for twenty cents an hour and a "fifteen cent man" will work for fifteen cents an hour.