This paper provides a comparative evaluation of the total cost for six conventional urban sewage processing units (complete-mix activated sludge, extended aeration and oxidation ditch, with either belt filtration or sludge drying beds for sludge dewatering respectively) as well as for two types of natural processing ones (waste stabilization ponds and horizontal flow subsurface constructed wetlands). This cost analysis emphasizes on cost components, such as construction cost, energy and chemicals costs, maintenance expenses and salaries. Analysis and estimation of cost functions was based on typical Greek cost prices. A percentage analysis of the total cost components is carried out and results for various treatment types are compared. Estimated results are compared to fiscal data collected from units in Greece.