Create magento block to display categories and subcategories in dropdown

We have a website selling car parts and need to create a product finder that will narrow down the navigation time for the customer and not put too much load on the server. See example here of what we want to achieve: [login to view URL] Our aim is to have a category for each car "make" and then you drill down to the subcategory of the "model", then the list of all "submodels" (CHASSIS / ENGINE # YEAR) to appear on the results page as per the example. And finally the customer can select their particular submodel and view all the products we have to suit their car. We would like to hear your suggestions on what solution you propose and will choose the winning bidder accordingly. The output needs to be styled well and fit with our current website theme which I will share upon request.