"Expensive keyword" (high CPC) isn't equal to "profitable keyword" (high earnings) due to the low volume of traffic expensive (niche) keywords produce. The best way to find really profitable keywords is to rank keywords by cost/day (cost per click X clicks/day) rather than cost per click.

Almost all AdSense publishers are looking for the most expensive keywords. Let's have a look at the top 100 most expensive keywords. But first let's add 2 extra columns to the list: clicks/day and cost/day by Google AdWords estimation:

selling structured settlements
cash for structured settlements
auto insurance quotes florida
california auto insurance quotes

Have you noticed that keyword price result in ZERO profit if there are no clicks? It's cost/day (keyword price X clicks/day) that makes you rich, not keyword price itself.