Advanced search and set a category to paid. Custom PHP script.

I have a craigslist type site setup and running here: [login to view URL] Need to add an advanced search box under the normal search box and on category pages. A dropdown menu (on the left sidebar just below the category dropdown menu), where the user can select the specific place (from the ones that I added in the admin area) or "All Cities". Below that we make an "Advanced Search" button, that will open a search box where not only the cities or "All Cities" can be ticked, but also all the categories and/or sub categories. This "Advanced Search" button should also be present on the other pages where users can search. Another thing is that in admin area I want to be able to set certain categories to paid so user has to pay if they want to post in that category. Let me know if you have any questions.