Note: in this question I'm considering cost in both money and fuel terms, and looking for answers that consider both.
So we know that using chemical rockets to reach the moon, or further into space, costs hugely more in fuel, weight, and money terms, than just aiming for low earth orbit.
That raises a question - how do the fuel budgets and economics work out, if we spent fuel and money to create a low earth orbit starting point for further exploration, and bring fuel and rocket components there from earth, as opposed to doing it direct from earths surface?
(Note that if our deeper space exploration started at earth orbit, it wouldn't need to be nearly as massive as we are used to - it wouldn't need the same fuel or rocket systems, nor streamlining, nor protection against atmosphere. It could also return to earth locality for reuse by any gravity-aided route, however slow and leisurely the route, taking months or years to do so if uncrewed, reducing return/deceleration fuel delta-v needs (on crewed ships, life support on average I guess adds less weight than extra fuel to shorten the trip, so a slow return would be viable?). Equally our earth-to-orbit delivery rocket wouldn't need the kinds of crew protection needed for longer travel in deeper space. So the ships involved are very different too, which makes a big difference as well, I suspect.)
By analogy, when we climb an Everest, usually we don't try to do it direct from our hotel in the nearby town. We create a base camp, lug our gear there, and set off on our more challenging and demanding expedition from that base camp, not from our hotel.
What are the practical fuel, money/investment, and weight implications, when the two methods are compared for space exploration?
If a LEO "base camp" is better, are two (LEO and further out) even better, or do they hit diminishing returns?