The threshold
There's somewhere between suborbital flights (affordable to tourists who pay the whole thing) and low earth orbit, a limit that makes it very difficult.
Perhaps, a way to reach that limit is to build an air-launched rocket capable of putting 2 to 4 tonnes into space!
There's a carrier to build (which could be used for other kinds of transportations) and a rocket (re-usable or 2 expendable stages).
It would be NASA's role to make it possible.