That sounds like an unnecessarily complicated way of going round things. Just buy a router, set it up with WEP encryption and MAC filtering so the only people who can use it are those who you have given the password to, and who have given you their ethernet card's MAC.
Divide the cost of your internet service by the number of people using it (yourself and whoever else). Don't get into the bother of charging them one month on, one month off - if they want a share of a domestic internet connection then they should be prepared to pay a portion of the true cost of that connection always being there when they want it.
If they want internet cafe-style access, tell them to buy a laptop and spend the evening in your local Starbucks.
