As part of that research, I ended up purchasing a list of the top 50k paying keywords off a shady looking website. The site only took PayPal, and they were only charging 50 bucks, so I figured it was worth it, and I wasn't risking too much aside from exposing my PayPal account, so I bought it.
I was pretty skeptical of the data at first, but I randomly spot checked around 50 search terms, with my Adsense account, and they seemed to correlate pretty closely.
I then wrote a script to cross reference how much people were paying for each set of keywords with how many results were returned for those keywords. That gave me a ratio of High cost keywords::number of results, which was enlightening.
Mind you, this data is suspect. Google doesn't charge a fixed rate for their advertising rates, from what I understand, each time an ad is served, the price essentially depends on an auction and the price varies accordingly. Also, I bought this data off a shady looking website during a really low point in one of the worst economies in decades. Caveat Emptor
That being said, I thought you might find it interesting.