Advertising expenditures, media expenditures, advertising spending, ad spend, or even "adspend"...
These are all phrases used to answer the question: How much did Company X pay for advertising?
Below are several sources you can use where you will more consistently find some data on ad spending. These sources are best for snapshot data, not for time series.
Be aware that ad spending is often not disclosed in any detail. Only public companies are required to do so, and only under certain circumstances (ad spend greater than a certain percentage of total revenues). Companies get to choose how much detail they will disclose, and some companies regard this as proprietary information (i.e. not for the public).
Advertising rates, or, How much does it cost to place an ad?
Advertising rates are often determined in negotiations or on exchanges. Print media such as consumer or trade magazines and newspapers still provide "rate cards" and "media kits" that offer standards advertising rates and audience demographics. Digital properties, such as websites, online news sources, cable, video and television, often make audience demographics available via "media kits", but not rates.