There are several good ways that you could find journal articles that cover studies that have been done on the economic status of white prisoners. You can do exploratory searching using Google Scholar (like this one)and take note of the articles and journal names of interest - then using New York Public Library's catalog, you can look up whether the library has the journal.

Another, more targeted, approach is to go into the library (the SYBL business library branch) to use the electronic journal article data base called "Public Affairs Information Service (PAIS)" - you can plug in the phrases "*Crime and criminals - Economic aspects" and "Prisoners -- Economic conditions" as searched in the "Descriptor Field".

I tried this and got the following promising looking article from the journal "Corrections Management Quarterly":

Henry, D. Alan. "The impact of financial conditions of release on jail populations." Corrections management quarterly 3(1999):28-34.

Lastly, you can get good summary statistics of prison populations and various socioeconomic variables from this page at the US Department of Justice