HI Send2
I have done what you are asking and here are my findings.
Adsense for most publishers, make about 0.50 per click.
Adwords costs approximately 0.50 per click
1 for 1 if you have a 100% ctr which we know you don't.
at a 20% CTR you will spend $2.50 in Adwords to make 0.50 in Adsense.
If you can get the CPC down to 0.05 then you could maybe break even.
Yahoo also costs about 0.50 per click and Ask.com is at 0.25
7search, abcsearch, mamma, etc do not send very good traffic even though they may less expensive. If you have seen the site their ads appear on you would not be quick to buy their services.
So your answer in my eyes is to not to bother.
Even if you found high paying keywords in Adsense such as mesothelioma... you'll also pay through the wallet in Adwords to get clicks.
Stay with
SEO and viral marketing for Adsense.
Hope this helps.