9- Cassini–Huygens- $3.26 billion
Number nine is an unmanned robotic spacecraft sent to the planet Saturn system.
Cassini-Huygens was launched in 1997 after nearly two decades of development. Cassini had the privilege of being the forth space probe to visit Saturn and the first to enter orbit on which it landed in 2004.
The two-part spacecraft is named after astronomers Giovanni Cassini and Christiaan Huygens.
This year, NASA reported that evidence of a large underground ocean of liquid water on Enceladus, a moon of Saturn, had been found by the robotic spacecraft.
The costs? The costs of searching and exploring the second largest planet in our solar system, has not been cheap.
Total costs of the mission were estimated at $3.6 billion which was divided among NASA, The European Space Agency and the Italian Space Agency.