This link gives some catalytic converter content;
http://www.hpcnet.org/sdsmt/SiteID=199458
It states;
In general there are three types of automobile catalytic converters in terms of the PGM content. Grade 1 consists of 2200 parts per million (ppm) of platinum (Pt), 200 ppm of palladium (Pd) and 300 ppm of rhodium (Rd). Grade 2 has 1000 ppm Pt, 200 ppm Pd, and 100 ppm Rd; while Grade 3 consists of 875 ppm Pt, 250 ppm Pd, and 30 ppm Rd.
On the average a metric ton of each catalytic converter grade contains the following PGM values: Grade 1 - $34,588; Grade 2 - $16,023; and Grade 3 - $13,667. These values are based on March 13, 1998, metals market prices of platinum at $392/oz., palladium at $264/oz. and rhodium at $535/oz.
With approximately 700 catalytic converters producing one metric ton of materials, over 21,400 metric tons could be obtained from the 15 million autos that are junked annually in the United States. With a current average value of $21,426 per metric ton for the three grade types (based on March 13, 1998 prices), over $450 million worth of platinum-grade metals could be recovered from these used catalytic converters.
Also this article was from 1998, so take that into consideration also,
that is probably the age range you will find in junkyards anyway, except for wrecks. And the precious metal prices mentioned will have to be updated to figure the current per ton prices.
Jim