The proposition of an application actually makes this seem easier to accomplish. All the application really needs to do is turn on the hotspot, grab the syn packet, and send an ack packet to the connecting device once the payment is confirmed. That would be really low overhead in regards to battery drain on the phone and the app wouldn't require much in the way of coding. Coding for various OS's would be a bit time-consuming, but not nearly so much a coding custom firmware for thousands of routers.

So, to break it down into layman's terms starting from discovery:

Download the application (wallet integration perhaps to make this exceedingly simple for new users?).
Launch application and allow user to choose between connecting to a hotspot or hosting one (search features such as preferences for speed, ping, price, etc. for priority searches, likely later in lifecycle post-launch).
If hosting, specify price, connection time, allowable connections at once, etc. Profit.
If looking for hotspots, choose hotspots visible in-app (bluetooth tethering for phones? Proximity map updating frequently to show nearby hotspots? Stretch goals!!!) and unlock wallet, send payment, wait for confirmation, do web stuff.

Look about right?