If you could gain access to NASA's info on past projects such as NERVA, and ignoring any and all political red tape - maybe a few billion dollars would do the trick. I think it would be best used as an upper stage. But again if you could ignore the public opinion then a large HLV isn't out of the question.
If it was the end of the world, just build a super orion colony ship and get out of dodge! I'm certain even then someone would protest the launch.
that should minimise the number of ruffled feathers.....
Concept : use electric power from a nuke plant to fire a multi-megawatt laser beam at the belly of a shuttle craft fueled with hydrogen propellant (only), like an NTR.
Launch is by way of maglev or scram-accelerator, from high-altitude launch site. Laser is located a few hundred miles down-range.
Muzzle is aimed near-vertical, to get out of high-density atmosphere as quickly as possible.
Hypersonic-waverider-type vehicle performs aerodynamic turn in upper part of atmosphere, to convert vertical velocity to horizontal, with minimum losses (high L/D design). Laser heating of propellant heat exchanger on belly provides remainder of thrust required for orbital insertion....