> SpaceX does not say how much Starship is costing them to develop, but external estimates seem to be under $8 billion. So for the cost of 2 SLS flights, SpaceX is developing a rocket with a cost to LEO orbit of under $10 million, and that they are aiming to get down to $2 million.

Some of that sounds like unreasonable optimism.

Given the track record of SpaceX, it's safe to assume that Starship will eventually fly and that the lower stage will eventually be reusable. Getting the Starship itself to survive reentry and landing in good enough condition to fly again without major refurbishment is another story. Something like that has never been achieved before. It's plausible that SpaceX will make it happen, but it's also plausible that it won't work. Then Starship will be simply an expendable upper stage that's too big and too expensive for the purpose.