A joint study conducted by NASA and the European Space Agency (ESA) shows that a humans to Mars program based on the Mars Direct mission plan is affordable.
NASA costing models show that the Mars Direct plan could be implemented for a cost of $39.4 billion for all hardware development plus the first mission, with each follow-on mission costing an additional $7 billion, while ESA costing models show Mars Direct costs for development plus first mission as $26.6 billion, with each follow on mission costing $5.2 billion.