AdWords uses a cost-per-click model (CPC model). For you, this means paying each time someone clicks on your ad. Which is why it is worthwhile researching the relevant search terms, as they can impact the effectiveness of your campaign. By advertising on the right search terms, you'll rarely pay for visitors you aren't looking to target. What if the campaign isn't such a hit? Not to worry. Your AdWords campaign can be tweaked whilst up and running by adding or removing search terms, for example, so you can keep pursuing the best results at the lowest prices.
Google AdWords does not specify any run times or prices in advance. It is possible to set a maximum price per click and a daily budget. This gives you control over how much you spend on the campaign. AdWords works along the following principle: the higher the bid, quality score and budget, the higher and more frequently an advertisement is displayed in the search results. The budget can be adjusted and the campaign terminated at any time if, say, you have managed to find the talent you were looking for. Rest assured that your budget will always be well spent!