I will be building a classified ads website for a specific niche.
I am wondering if I could have a search box similar to autotrader.com,
where users could select a make, model, location, price, etc..
ClassiPress has an advanced search functionality where you can allow custom fields to be searched (i.e. select from dropdown items, make, model etc). An example of how this works can be seen on the ClassiPress demo site in the category sidebar. Moving this functionality to the main index page would require customization on your part. Thanks.
The only dynamic dropdown option occurs during the initial category selection, so if you happen to set up the make and models as categories and sub-categories, then it would work this way, however if you add them as fields within the custom form, then it will not. Thanks.