I basically cloned the Bingo Card Creator idea in that I sell access to a PDF generating machine. I though long and hard about a recurring fee model, but decided that my customers are price sensitive, and to be fair, I'd have to charge $5/month rather than a one time fee of $30. Sure some people would sign up and continue to pay, but most would cancel after one month and I'd only get $5. I know this because 90% of my customers never log in again after one week.

Additionally, I think a recurring fee would scare customers off in this market, and I go out of my way to tell them it's a one time fee and that they get access forever. If you're wondering, "Do some of them feel a sense of entitlement for essentially... forever?" Oh boy yes, they do!!! But that's OK, I treat them real nicely anyhow.