That’s what usually happens causing turn down of a lot of great ideas. But there is a solution. CREATIVITY. Here is a perfect example from AlmapBBDO for Volkswagen brand in Brazil. They did their part offline and then just placed the video on Youtube and cleverly related their message to the already existing Youtube functionality. In other words, no actual need to spend money on preparing banners as the message goes out to the online audience through already existing free online media channels.
Have a look at the video below: