The High Cost of Poverty: Why the Poor Pay More. "Having Little Money Often Means No Car, No Washing Machine, No Checking Account And No Break From Fees and High Prices" Read the article in the Washington Post here. Thanks to Justin Briggs for finding this article.
Here's a related study: Neighborhood Financial Services: An Analysis of Supply and Demand in Two New York City Neighborhoods. From the New York City Department of Consumer Affairs Office of Financial Empowerment.