I've thought about doing something like this for a long while. Finally I had an apartment complex a couple years ago that allowed you to pay online (e-checks only), so maybe the industry is finally ready for this.

Expect a lot of resistance to landlords letting tenants pay with anything but e-checks, though. Think about adding something like automatically sending out emails to tenants to remind them to pay the rent (opt-in on first payment)?

Oh, and I think you might be underpricing yourself.