If you use Google AdWords to advertise there is a cost per click bidding system. You pay only for clicks on your ad and the cost for the ad varies depending on the keywords use for the ad. So, the cost will depend on how much you want to spend per ad and how much you authorize on a daily basis.
To advertise your website or business on Google's advertising service, you will need to set the amount you would like to use for your advertising. For more detailed information, go here: www.google.com/AdWord.