Which plugin to use? For the client?

Hello, Happy New Year everyone.

Right, I've got a new client and they are after a really tricky search functionality and I wanted some advice as to which plugin would be best. Ideally here, but if not elsewhere.

The client is after a search function for an e-commerce store for diamonds but it needs to be similar to that of these sites below;
http://www.mydiamonds.com.au/diamonds/search
http://www.77diamonds.com/classic_rings.html

Any ideas or advice greatly appreciated.

Kind Regards

Jimmy