Needed: Feature: Drill down through category terms to listing of tagged content

I need help finishing functionality on a Drupal 5.7 web site. I have two content types, business listings and banner ads, and a hierarchical category comprised of states, its areas, and their cities, like so:

• New Hampshire
  • Bedford Area
    • Bedford
    • Dunbarton
    • Goffstown
    • etc...
  • Claremont Area
    • Acworth
    • Charlestown
    • Claremont
    • etc...
  • etc...
• etc...

Users need to be able to "drill down" through category terms to find their city. For example: the user begins with a map of New England. They click on New Hampshire to bring up a list of areas. They click on "Bedford Area" to bring up a list of cities. Finally they click on "Charlestown". Having chosen their city, they're taken to a page which aggregates all the content tagged with it--business listings in one column and banner ads in the other. They will print this page.

This is the basic functionality. There are some enhancements that would be nice depending on the amount of time and money involved in implementing them. I assume this will require a custom-built module, though if you think it could be done using contributed modules I'd like to hear your proposal. My client is in a hurry to launch, so I need help fast. Please contact me if you think you can do that job, and we'll discuss the price.

Thanks,
Travis