At the coffee shop I frequent, with your purchase you can get a card for 2 hours of WiFi. This seems like a good way to limit your laptop per dollar ratio.
In this case they don't charge for the WiFi, it just comes with your coffee.
My reasoning is that most laptop users will use WiFi, and if they want to use it, they at least have to ask for a new card every couple hours, which involves either buying something or overtly seeming like a leech.