An average 30-second spot on ABC's Grey's Anatomy costs $419,000 -- making it currently the most expensive on primetime television, according to a survey by Advertising Age. The figure tops the $394,000 that spots on ABC's Desperate Housewives were being sold for last season. Because of slipping ratings, rates for Housewives dropped 31 percent to $270,000 this year, putting it at No. 4. The runner-up to Grey's during the current season is NBC's Sunday Night Football, where spots are going for $358,000. And although it, too, has been witnessing a ratings decline, The Simpsons came in at No. 3 with $315,000 per spot. Rounding out the top five, Heroes landed at No. 5 with $296,000. AdAge observed that come January, when American Idol returns, spots on the talent show are expected to dwarf all others, fetching $500,000 to $700,000 each.