Banner impressions: you buy banner exposures. That's very cheap and has no guarantee how many times the banner will be clicked on. You usually buy those if you want your brand to be known. Regardless if many people will click or not, you want people to see your logo or company name everywhere.
500,000 impressions = 25 U$
1 million impressions = 50 U$
5 million impressions = 240 U$
10 million impressions = 450 U$
50 million impressions = 1,950 U$
That's for banner size 468X60 - max. 15k
Other sizes are possible: the smaller, the cheaper (250X72 80%, 180X100 60%, 120X60 50%, 88X31 20%) - but also slower to deliver and usually lower click rate.
