Advertising space is a lot like airplane seats. If there’s nothing in it when the time comes, then its value goes right to zero. So, publishers have every incentive to get “butts in seats” at any price. This ad space in danger of expiration is referred to as remnant inventory, making it sound somehow inferior to other ad space. Smart shoppers know better.

If you’re one of these smart shoppers interested in radio, consider using bid4spots.com, one of the two largest radio advertising exchanges (and now partnered with eBay). How does it work? To buy ad space, you create a “reverse” auction (see this detailed demo), by setting a ceiling price for ad space, while also indicating the specific stations / geographies, day-parts, ad lengths, and other details. Radio stations then will bid to sell you the ad space, with the lowest bid (meeting your requirements) winning the deal.

The site notes that with multiple stations competing for advertiser dollars, sometimes spots go for as low as $10 (rates/CPMs have generally been 70-90% lower than the regular rate card). Remember, one way to improve the ROI of your marketing investments. . . is to reduce the I.