There is no answer to that question because Google determines the amount every single time the ad is served.
It depends on the particular word. Some words such as "lawyer" and "seo" are very high, some such as "red raincoats with ear protectors" are probably not as well paid.
Exactly, some words very high paying and other are very low. If you do a quick forum search you will come up with several high paying keywords. BTW Notting, can't you find better example of low paying keyword?
The most I have gotten in one click was just under 2 dollars on my credit card website. But on my other sites I average about 20-30 cents per click.