Many agencies involved for such type of desalination plant installation , Detailed information available on line. However similar question was already discussed in Research
The question is addressed in several research articles on desalination of seawater. But, the answer depends on the type of technologies used in desalination of seawater. Therefore I propose the following articles that represents The most profitable and low investment technology and very low cost of desalination of sea water.
Adel OUESLATI, Ahmed HANNACHI, Mohamed ELMAAOUI, Experimental Analysis of Air Humidification by Brackish Water in an Adjustable Height Packed Column Humidifier Operating on the Principle of an Air Lift pump. International Journal of Chemical Engineering, Vol.30, Issue 1. PP 1 1103-1110.
Oueslati A., Hannachi A., Elmaaoui M.; Effect of air humidification on the pumping efficiency of water in a packed column humidifier; Energy Procedia 74 ( 2015 ) 1381 – 1393.
a colleague of mine did his PhD on Simulaiton different CSP&Desal Plant configruations last year. There you should find different kind of cost structutres as well as strategies for plant operation!