“American Idol” will go where no show has ever gone before this season: past the $700,000 mark for a 30-second ad.

The Fox singing competition will become the most expensive regular prime-time series in TV history when it returns in January, with a 30-second commercial on the Wednesday edition of “Idol” costing $705,000. No show has ever broken the $700,000 mark before.

“Idol” is also the second-most expensive show on which to buy ad time; spots on the Tuesday edition will go for $660,000, according to a survey of prime-time ad rates by Adweek magazine. The premium prices reflect “Idol’s” position as the most-watched show on TV, both in overall viewers (where the Tuesday edition actually ranked first last year) and the advertising sweet spot of adults 18-49.

ABC’s “Desperate Housewives” is next on the list, commanding $560,000 per ad – a huge increase over last fall, when it was an unknown quantity and fetched about $200,000 per spot. Its breakout success also helped fuel ratings for Sunday-night companions “Extreme Makeover: Home Edition” and “Grey’s Anatomy,” and those ratings are reflected in the shows’ ad prices. “Home Edition,” which also offers prime product-placement opportunities, now gets $355,000 per 30-second spot, while “Grey’s” pulls in $440,000 – more than double what it cost to advertise on the series last spring.

“The Apprentice: Martha Stewart” is the most expensive new show on the fall schedule at $310,000 per commercial. The Donald Trump “Apprentice,” which has always enjoyed a strong concentration of affluent viewers, clocks in at $350,000, a decrease from last year that mirrors the show’s drop in ratings.

UPN is getting $179,000 for ads on its highly touted new comedy “Everybody Hates Chris,” a record for the network.

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