Howard Hughes was paid $23 million ($300 million inflation adjusted) to develop the Spruce Goose. It was the largest airplane in the world at the time. It did not fly until after World War 2. Hughes had to fly it because the US government said he was a war profiteer who took money but did not deliver a working plane.
One hundred times more money could end up going into a rocket dead-end with the Space Launch System.
$35 to $40 Billion to Get to a First Integrated Launch of SLS and Orion
From 2005 to 2010, there was about $11.9 billion spent on the Constellation program. This was paid to mainly the same companies working on Space Launch System. They were adapting the same Space Shuttle boosters as the SLS program.
Space Launch System (SLS) has spent $14 billion from 2011 to 2018. It will spend another $6.8 billion from 2019 to 2021. There is about $2.3 billion per year being spent on SLS. It will $21 billion on SLS to get to its first test launch if the test launch happens in 2021.
$15 billion has been spent on the Orion crew spacecraft. There is $1.3 billion per year being spent on Orion. There was one pad abort test in 2010 and one orbital test on a Delta IV rocket in 2014. There will be one more unmanned test currently scheduled for December 2019.
A combined Constellation and SLS spending of $26 billion has resulted in one test launch of Ares 1 in 2009.
Orbital SpaceX Starship in Late 2019 or 2020
The first orbital test launch of the SpaceX Starship could happen as early as late 2019. SpaceX is talking about 2020 for the first test launch.
A SpaceX Super Heavy Starship will totally outclass the Space Launch System in every metric.
SpaceX Heavy Will Have Two Launches Early in 2019
SpaceX Heavy will have two launches early in 2019. This will show rapid re-use of the first stage boosters.
SpaceX Heavy comes close to the heavy launch capabilities of the Space Launch System. If four side-boosters were used instead of two, then SpaceX Heavy-4 would outlift the SLS.