Victor Stango of UC Davis Graduate School of Management has written Are Payday Lending Markets Competitive? Regulation (Fall 2012) at 26. Here's the abstract:
The rapid and widespread growth of the payday loan market has sparked considerable controversy, in part regarding the “high” prices charged for these loans. This article presents several new pieces of evidence addressing this issue. Specifically, it finds that credit unions — who frequently are payday lenders’ sharpest critics — do not (and apparently cannot) offer functionally identical products at lower prices. It concludes that the claim that other lenders can serve this market at lower prices does not seem justified.