As Janie says, the subject is not simple. The stereotypical views of the poor white no longer hold and the situation outlined by WYSIWYG belongs to the past. The conditions in "To Kill a Mockingbird" belong to the past.
Both Blacks and Whites from lower income strata now constitute lower level police cadres in small towns as well as cities in the South.

A few points without documentation- internet articles will fill in the facts and statistics for you.
The women and men who worked in the mills have mostly gone, as their jobs have moved offshore. They now work in Walmart, MacDonald's, Target, etc. One-mill small towns have lost the young people as jobs vanished.
Machines harvest the cotton and corn. Small family farms are disappearing. Some migrants work perishable fruits and vegetables, but they tend to work over large distances- Texas one month and Washington the next, etc. Many have been replaced by immigrants who are more easily 'controlled.'

Many poor whites, like Blacks, moved to the cities of the north and mid-west to seek employment. Problems developed- they had a hard time integrating with labor there, and they were regarded as undesirable and destructive by managers of rented premises, much more so than the Blacks who often had settled relatives to help. They became well-known in the criminal courts. This, of course, also has become problem of the past.
As late as 1970, the South had 46% of the nation's poor,* Negroes three-times as likely to be below the poverty line but were fewer in number; over 6 million poor whites in the South in 1970, some 60% outside metropolitan areas.
-Important article but out-of-date: "Some Rural Economic Development Issues in the South," The American Economic Review, vol. 1/2. 1972. This should be available from a good library.

Don't forget the military services, a major employer of young men and, increasingly, women. Education levels have improved although still not good; areas such as rural Maine are no better.

Don't forget the importance of the Military Services as an employer of young men and women from poor and rural backgrounds.

Many sociologists now maintain that the South is no longer distinctive. Scholarly books ...(recently)... make the point that "the idea that the South is exceptional, a region apart from the rest of the country, is no longer true." A lot of the regional differences have disappeared as the present day is approached. To make this point, a book being prepared by Lassiter* and Crespino is titled "The End of Southern History."
*Univ. Michigan. See the article in NY Times- "Interpreting Some Overlooked Stories From the South," by Patricia Cohen, May 1, 2007: Interpreting South