That is a far more difficult question to answer than first appears.
Click through optimization runs anywhere from 5 cents to 50cents per click depending on the keyword. The more targeted but valuable phrases go higher. Highest I've heard was $1.05 for a specific combo of "kelly blue book" and certain make of "suv".
High traffic 'fluff' words go for alot less. This like top movies, or infotainment words (mp3, singers, xmen, etc) go for a bargin price.
Straight away Optimization? Hard to say. I almost won't take any of that work anymore. People still expect the stars and you give them the moon and they aren't satisfied. If you work on click-through, there are no doubts about performance - it is all right there in the logs to see and the customer only pays for what they get. I really like working on click-through basis - it takes all the guess work out of tracking and puts all the "noise" in park.