International Space Station (ISS)

According to some estimates, the International Space Station (ISS) is the most expensive single item ever built. The project was originally projected for $150 billion in 1998, making it the world's largest megaproject at the time. The space station, a cooperative project produced in conjunction with 15 different nations, is longer than a football field and was meticulously built piece by piece while in orbit using spacewalking astronauts and robotics in 30 flights over ten years.

The station's cost has only continued to rise as the project's lifespan lengthened and additional parts and equipment were added–a cost overrun that should have been avoided in the planning stage. In actuality, the station's total estimated cost will be at least $230 billion by 2030, when it is expected to be completed. Some speculate that the eventual cost will be closer to $1 trillion, dwarfing comparable space construction projects such as the manned Mars trip, which is expected to cost only $40 billion.

Cost Estimation: $230+ Billion by 2030