I make about $300/mo with https://broker.mapthatpad.com. Not even close to what I originally was intending (and the amount of time I've spent building it) but to be honest, I have not been doing a whole lot in terms of marketing and selling it at the moment.
I hope to do more selling/marketing in the future and get this monthly number higher.
Its a monthly recurring model. I actually partnered with a small company in NY that sells a tangential product to the same market. They do the marketing within the NYC market for me.
I can try to sell this more actively to other markets, SF being next since I live here, but with a full-time job and a baby, its hard! In terms of marketing, I think I could manage a small AdWords budget to run but it would initially be more just me cold calling and setting up demos - starting with smaller shops with a shorter sales cycle first.
I hope to do more selling/marketing in the future and get this monthly number higher.