$600? where are you looking? try ebay...
http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&fkr=1&from=R8&satitle=york+compressor&category0=
or any auto part store... for a york 210 of of a 78 ford econoline van... and you will either need a v-belt clutch or a serp clutch depending upon your vehicle. i spent around $300 for both of the ones i have gotten, one for myself and one for someone else