Ice is both the most efficient and the cheapest. If you chill to ~110°F and then add a gallon of ice (sanitary frozen water bottles or whatever, it will drop into the mid-60s.
BTW, here’s the search link: http://www.homebrewersassociation.org/forum/index.php?action=search
It’s the third from the left in the top navigation. Google is even better: efficient chiller site:homebrewersassociation.org - Google Search