Do not worry - AdWords
puts you in complete control of your spending.
There is no minimum spending requirement; the amount that
you pay for AdWords is completely up to you. For example,
you can set a daily budget of five pounds and choose to pay
five pence each time your ad is clicked.
We provide keyword traffic and cost estimates so that you
can make informed decisions about choosing keywords and
maximising your budget. (Estimate keyword costs)
Pay only for results
You are charged only if someone clicks your ad, not when
your ad is displayed.