Setting up something on your own is sort of complicated, as you will find when you try it.
There is a complete solution, with a Linksys WiFi gateway router running (no doubt) DD-WRT software, and they provide the software for a computer to do the revenue gathering. The total cost of this solution seems very reasonable at just under 100 bucks (less if you want to buy the router and load the required router firmware).
This outfit takes 25% of the revenue, you get 75%, not a bad deal for doing very little except installing the hardware and getting back to something more interesting.
http://www.hotspotpa.com/hspainfo.aspxI hope this information at least gets you thinking of some solutions. This one looks good to me, but there may be others just as good or better.
Jeff