Basic Product Sorting / Filtering script

A website I frequent has a number of products in their clearance category. Over the last year or two I'd say they have about 10,000 products in this category on average. Sometimes these products are in the clearance category, but there is no sale pricing on the item (it is sold at list price). When the product is on clearance, it will say in Red font Clearance, then list the price and have the retail price crossed out. The site allows me to sort from Low to High, High to Low and a few other things but does not allow me to exclude non-clearance priced items, and also does not allow me to sort by discount %. I would like a script of some type to be able to filter their website and display only the things I want to see: 1) Remove all products that don't have a clearance or sale price 2) Sort products by the % discount To clarify this filtering / sorting would be done on an external website (or even processed on a local computer), and you would NOT have any access directly to the database.