Add a custom form and sort page to Drupal

There are lots of different ways you could solve this. One includes writing a custom module for Drupal. The first idea that comes to my mind is to use CCK with a custom content type to hold each diamond object. The Views module would provide listings and filters. You'll have to do some theming and maybe some code customization, but I think you could do most of it with very little new code.

If you're talking about the Search for Loose Diamonds system you could easily create a series of taxonomy vocabularies to take care of this. Then create nodes for the individual diamonds and apply them to the right terms. Then you can use the views module to create a drill-down system like what you currently have to let users choose what they are looking for.

The only function here that I am not entirely sure how to duplicate in Drupal is the Best and Lowest ranges you use for Clarity and Color. There may be a way to do this with Views, but I have not seen it as of yet.

What you can do is use a select list instead of a dropdown and allow the user to select multiple values. This would actually allow greater functionality for the user as they could view all asscher and cushion with a certain range of color and clarity as opposed to only viewing one choice in each criteria at a time.

Sorry if that is a little fuzzy. If I need to clarify let me know.