I think you've almost got the market. My bet's on small (or just remote) towns with only one or two banks with limited hours coinciding with where the communal

I think you've almost got the market. My bet's on small (or just remote) towns with only one or two banks with limited hours coinciding with where the communal laundry services only accept quarters and the blasted change machine is always out. (These are the sorts of places where a vending machine that accepts cards would be a cool novelty.) I'd actually be interested to see how many people live in that kind of rural America versus large cities. My college suffered from this, and I had a number of late nights where I was perfectly willing to pay two dollars for a buck fifty in quarters, just because there wasn't anything open in walking distance to get quarters. As far as I've seen, the same places with these communal laundry services also tend to have many mailboxes consolidated in one place. These'll be locked, so the package of money is fairly safe, assuming it gets through the postal service safely.