Classifieds website with multiple cities

I am looking to create an automobile classifieds website that contains 20 major cities in the US with two category levels. Each city will have the *SAME* categories. Car engine parts |- Fuel injectors |- Pistons |- Spark plug |- Crankshaft Car brake parts |- Brake rotors |- Brake pads |- Brake lines When users visit the website, they should not have to login. Instead they should be able to freely browse into any city they want, and see the SAME categories. When they click into a category for a certain city, say Houston, they should see all the suppliers for that category in Houston. If they browse to a different city, they should see a different list of suppliers for that particular city. All the supplier's contacts and data should be entered by the admin only. (Future versions may allow users to post such data) This is kind of like multiple cities' classifieds rolled into one website, with the same categories in each city. The solution can be: 1) Pure custom code, or 2) Some custom code mixed with other open source projects, or 3) If you feel that the purchase of a 3rd party extension/code/software can get this job done, that is acceptable as well, of course we will need to verify first before we commit to using that 3rd party application. We prefer the solution to be an open sourced CMS such as Drupal or Joomla.