USA local search engine

Hi everybody.
I'm developing a kind of a search engine, oriented to products and services for local users. For a lot of reasons I want to create subdomains for every state of USA. As my own site is still mostly in my mind, to get an idea of what I'm looking for - you can look here (this is certanly not the best example of webdesign and usability, BUT those guys made EXACTLY what I need from the point of view of subdomains).
So my question is the following: how is it better to configure DNS and web-server to make the same way (I will use linux hosting). Truly speaking I know how to make it working for 3-4 subdomains but if we make 50 different independent subdomains - the maintenance and support will by very dificult.
Thank you in advance.