SRDS Online
The best source for media advertising rates, whether broadcast or print, are the Standard Rate and Data Service Directories. You may not know that the University has a subscription to the online version of this resource (this will be the last year I stock the Circulation volume here at Annenberg). This resource is full of not only ad rates but in the newspaper section, for instance, it provides contact information, commission and cash discounts, general rate policies, black/white rates, color rates, insert rates, mechanical measurements, closing times, special positions, circulation figures, and classified rates. Similar detail applies to business publications, consumer magazines, radio, television, cable, and direct marketing. The SDRS database is available to the Penn community; you'll need your Pennkey and password off-site.