Multiple/Separate listings with 1 website

Hello, i have an issues with a site i am building… i am looking to put multiple searches within 1 domain but have them separate.

For example if you were to go to a automotive website, within 1 menu link you can search cars that have been submitted by dealers and private sellers through the admin after they register. And within that link the search directly relates to it as per the type of car, style, milage etc. Then there is another menu link next to it that has a different directory listing for auto services (tire shop, mechanics, etc.) in which users can submit there business through registering completely separately and control it within the admin.

I have played with the idea of mirroring sites under the same domain name but as sub domains. Anyone have any other clues how to go about this?