The average cost to you each time a prospect clicks on your ad. This is typically the payment model for Google Ad Words, Overture, Yahoo, as well as most other paid search companies. 

For most PPC search engines the average CPC starts at about $0.05 and can go in excess of $1.00 per click.  Keyword popularity, bid amount, and position will all influence the cost an advertiser will pay.

You should closely monitor your cost-per-click to ensure that you are not overpaying for your click-throughs. Each PPC search engine will provide you with the tools you need to create full PPC reports, which allow you to see your spendings.

Competition for a keyword might grow and as more people ‘bid’ on the same keyword you might notice that your CPC has gone up in price as a result. The more competitive a keyword is, the more you are going to spend on each click (visit to your site). This makes it very important to track how your keywords are performing and how much you’re spending on each keyword.

NOTE: Make sure  that the words you’re bidding on pertain to your particular business/industry or you will end up over-paying for words that don’t bring in the ‘right’ type of visits to your site. Keeping a well-targeted set of keywords will help you avoid higher  Cost-Per-Click spending.