i used an oil cooler from a 5 series BMW, around the same size as an rx7 cooler.. only cost me $50 but the support equiptment cost around $500 - lines, connections, remote oil filter, inline thermostat, sandwich plate..
pics of cooler
http://www.skylinesaustralia.com/forums/at...achmentid=13692
http://www.skylinesaustralia.com/forums/at...achmentid=13691
could do it cheaper without using same lines amd remote kits..
also depends on where you mount them on how well they work etc