Yes, there is a tool that you can use to see what advertisers are paying for the keywords. The link is
https://adwords.google.com/select/KeywordToolExternal I use this tool to research different keywords for my site so that I choose the more profitable ones to include for my adsense ads.
However, you can also use it if you are wanting to purchase ads so you can look for lower cost keywords that might bring you cheaper traffic.
Generally, the higher the cost of the keyword, the more the competition.
Hope this helps.