Google doesnt have any control over the prices.. ad keywords, locations it's showing, how many bids on that keyword, and the ctr of the 1st ad are all factors that affect the price.
1. Location 2. Keywords 3. How much time did the vistor who clicked spend on ur site and their site. mmmmm, I cant think of more now.. but hope this gives u an Idea good Luck
A lot of things determine your earnings. Page/site content Page Rank Originality of content Number of ad units being shown
This can help... but does NOT mean your going to get that per click. https://adwords.google.com/select/KeywordToolExternal?defaultView=2