This article from 2006-2007 doesn't say anything about the frequency of the ad... only the cost. Is this for one ad? An entire season?
ER NBC $282,000
Two & A Half Men CBS $275,000
Brothers & Sisters ABC $242,000
Dancing with the Stars ABC $229,000
The Nine ABC $224,000
American Dad FOX $222,000
The Office NBC $219,000
Earl NBC $212,000
Studio 60 NBC $210,000
http://www.frankwbaker.com/2006_2007_ad_rates.htm
It looks like those are per spot rates. For a national ad that reaches, say 1/3 of the country those are pretty good rates. Reaching the base vs reaching independents, moderate dems would, to me, determine where to place the ads, ie: 24 vs American Idol. The money would be better spent reaching those American Idol viewers.
Rates can go down for larger buys, it doesn't say if this is the open rate, or for a 6 week, 9 week, etc rate per ad.
Cheaper rates can be had by doing local or regional buys. Airing it in just select blue states...or those pesky 'purple' ones.
Also in this economy the is a surplus of airtime available, and that can bring the rate down.