A simplified analysis is presented in order to compare direct capture of carbon dioxide from air, i.e. air capture, and capture from fossil fuelled power plants. For air capture the literature shows conflicting data on the estimates of the costs of the technology, which range from 30 US$/t CO2 to $1000 US$/t CO2. This clearly creates uncertainty especially for those who have to implement long term policies to mitigate climate change. The aim of this contribution is not to assign a fixed cost to air capture, but to show that it is possible to make a common sense estimate of the ratios of cost and energy requirement of air capture compared to carbon capture from power plants. These ratios are at least 10 times for the cost and 3 to 4 times for the energy needed to produce a high purity carbon dioxide stream at atmospheric pressure.