Sure you can ask Adsense questions here, that's what this part of the forum is for.
I don't work with Adsense at all but know about keywords tools and used Adwords as an advertiser.
Why not go right to the source and ask Google what various keywords cost?
Then you can guestimate what you could earn on various KW.
https://adwords.google.com/select/KeywordToolExternal
After you enter your root keyphrase and get to the search volume page - then click show/hide columns and in the drop down select "Show Estimated Avg CPC" that will show you the cost per click.