The Superconducting Super Collider was famously cancelled in 1993 after running enormously over budget. According to the wikipedia page:
During the design and the first construction stage, a heated debate ensued about the high cost of the project. In 1987, Congress was told the project could be completed for $4.4 billion, and it gained the enthusiastic support of Speaker Jim Wright of nearby Fort Worth. By 1993, the cost projection exceeded 12 billion dollars. ...
What went wrong? Why was it so much over budget?
How can such a fate be avoided by future big physics projects in the US? What did we learn?