They also vary with the amount of money allocated per click and per day. Many of the google programs are pay per click, if a guy selling chess sets is willing to pay $5 a clickthrough, they will get more exposure than the guy selling penis enlargement for $4 per clickthrough.
Also budget is a factor. If an advertiser wants to spend up to $100 per day, they will get way more exposure than an advertiser wanting to spend $20 per day.
Since its pay per click, it can sometimes take alot of exposure to get those clickthroughs.
Repair #2 Pay per exposure
Active $20.00 / day 9 20,605 0.04% - $0.61 $12.48
the numbers break down as
For the last 7 days
Maximum of $20 per day 9 clickthroughs for 20,605 exposures .04% clickthrough rate average cost per 1000 exposures $0.61 for a total of $12.48 in advertising costs.
These ads generally run on places like the SDMB
Campaign #4 pay per click
Active $5.00 / day 3 4,085 0.07% $3.67 - $11.00
These are hits from google local and search engine sponsored links.