How to sell user names

Hi gang,

I want to create a membership website where sites are based on a football teams city name. So for instance I can only have one Chicago website.

Now the question is how do I present people with the option to choose from a list of cities that is available and remove the availability of such sites as they get sold.

So for example I start with this list

Chicago -- Register Now
Tampa -- Register Now
New Orleans -- Register Now

Then let's say someone registers Chicago and someone visits the registration page they are giving these updated choices

Chicago -- Taken
Tampa -- Register Now
New Orleans -- Register Now

Thanks