I've read all the answers provided and even though I think they are valid, I believe they miss one critical thing. The value of you obtaining a customer is not the $9.99 that you may get from them (or whatever you are charging), but the data you gather. In the financial industry to the contact is worth far more then anything you could ever charge a monthly fee for. The devil is in the details but I have lots of ideas on how you could monetize. We can talk further if you'd like.