There are a couple sites on the web of catalytic converter identification - Search "catalytic converters". Relative value is best determined by going to your scrap yard and get a price list for cats, specifically. There are a couple sites that list value, as far as that goes. If you send them pictures, they will identify and make an offer. Send the pictures to two or three different ones to compare their identifications and offers. Beware of scams.

You can compare pictures to what you've got and still misidentify them. This is an area where nothing beats experience.