To calculate television ad rates, take the SQAD cost-per-point (in US$) for market and multiply it by the Nielsen rating for the program that airs at the same time. That will equal the cost of the ad.
SQAD cost-per-point
x Nielsen rating
= (relative) TV ad cost
Daily Variety publishes a weekly TV ratings chart. Access that through the library (via Film & Television Literature Index with Full Text) (1994-2017)
Detailed notes:
Note: UNC does not have print or digital access to the full data collected by the A. C. Nielsen Marketing Information Company. This data is proprietary and only available to clients of A. C. Nielsen.