The USA forecast 8 billion dollars for a 6-month no-fly zone operation http://www.voltairenet.org/article169684.html

A study from the Center for Strategic and Budgetary Assessments (CSBA), published on 9 March 2011, assesses the possible financial cost for the USA to implement a no-fly zone in Libya.Extrapolating from the costs of previous similar operations conducted in Bosnia-Herzegovina, Kosovo and Iraq, the authors have estimated it, on average, at 10 USD per year and per square meter. As a result, a no-fly zone over the vast Libyan desert would prove to be particularly pricey.

The CSBA believes that the initial bombardment, which aims at destroying Libyan radars, anti-aircraft batteries and airports should cost between 500 million and one billion US dollars. Once this is done, implementing the actual no-fly zone should cost between 100 and 300 million US dollars per week.In six months, the bill would come to anything between 3.1 and 8.8 billion US dollars. This assessment only ponders the no-fly zone and does not include the cost of a possible ground invasion by US marines.Selected options and costs for a no-fly zone over Libya, by Todd Harrison & Zack Cooper, Center for Strategic and Budgetary Assessments, 9 march 2011, 8 p., 650 Ko.