You can go through an ad network, or you can find mailers who would do that for you. Payday loans (as well as dating, and adult industry offers) tend to do well on Yahoo (versus AOL/HM/GM or alike). You would want to set up a small test budget, and then move forward based on the metrics of those results. Pick out those who get you the best conversions.
I know that for us, we segment all data based on past history of clicks so that we can later run very targeted campaigns based on diet, ASOTV, homeowner, pet owner, etc.. I am sure others do as well so that when you send, you're sending to those who have some history of interest in those sort of offers (finance/payday/credit) helping to mitigate your risks and get you maximum ROI.
Honestly, that would give you the most targeted bang for your buck.
