The SLS rocket system will cost $7 billion to make, weigh 70 metric tons.
"Our nation is embarked on an ambitious space exploration program, and we owe it to the American taxpayers to get it right," said NASA Associate Administrator Robert Lightfoot, "After rigorous review, we're committing today to a funding level and readiness date that will keep us on track to sending humans to Mars in the 2030s - and we're going to stand behind that commitment."
Construction was approved after the SLS platform passed through NASA's "Key Decision Point C" phase. This phase of scrutiny is responsible for developing a budget ($7.021 billion), and a calendar for an initial launch flight. That flight is to take place in or before November 2018.
Of the estimated $7 billion-plus budget, roughly $2.8 billion has been marked as the contract for Boeing, who is the primary contractor on the SLS project.
The SLS is only one piece of the moon and Mars puzzle, as NASA is also busy building out the Orion spacecraft (the capsule that will ride on top of the SLS rockets), and the ground support/launch systems necessary for both hardware platforms to work.