1. Usually counted in cents per 1000 clicks or displays 2. A lot. I depends on the type of ad how much. 3. Html elements that are modified by the advertiser,

1. Usually counted in cents per 1000 clicks or displays 2. A lot. I depends on the type of ad how much. 3. Html elements that are modified by the advertiser, rarely some sites market the space by themselfs, then they can completly dictate the enviromnent. 4. You add a bit of javascript in the page that loads the ads from the server