Seeking an advanced search interface

I am looking for something that seems relatively simple but may not be and which I have been unable to find in any plug-in.

I want be able to extend WordPress’s standard search widget, to provide users with a more developed interface to search posts (I am using posts as product pages with eShop). Specifically, I want to have users search by select a manufacturer from a dropdown list, add a product name in a further search field, and a product number in another field again. The search is to be a simple AND of these three terms which are all simple text strings within posts – so the search is the same as that performed by WordPress, but it will make everything more user friendly and focussed for the user.

Using a search based on categories is a problem as there are a large number of product numbers. A search based on custom fields would become unwieldly again because a given product can have several product numbers associated with it.

It might be possible to take the data inputted from such a form and use code to input it into the existing wordpress search function. As someone new to that level of coding, I am not sure how to go about it.

Any suggestions would be very much appreciated. If you know of a plugin that will do the trick that would be great.

Thanks