I remember a number of interplanetary probes that had been cheaper and faster and sometimes better (NEAR, Mars Pathfinder, MGS, Lunar Prospector, etc...)There were failures but not as costly as Mars Observer.
I remember the involvement of NASA with Russia in spending months aboard Mir, in constructing the ISS.
I'm interested to see that had the Russians not been involved, the Soyuz capsules would not have allowed an american to stay aboard the ISS during this time.

The X33 was an attempt. Do we see today anything like trying to build a single stage to orbit rocket? Is there any money left for that?

Raoul