cough https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Metha... cough

Bah, this is the way: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

(Unfortunately if you do launch from Earth, neighbors will likely by a bit annoyed).

Now estimate how much that propellant will cost per kg of payload to orbit.

The problem with expensive launch in the past wasn't due to propellant cost.