I know its not very complicated but in my opinion a lighter than
air platform would be much better.
with todays carbon fiber composite materials the platform could be much lighter and much stronger than steel.
http://en.wikipedia.org/wiki/Carbon_fiber 
you could lift a payload to a high altitude , where much less thrust or force would be needed to reach LEO , then the payload which could be a remote vehicle could lift into LEO.
when a saturn 5 rocket lifts off its weight alone is
6,699,000 pounds (3,039,000 kg)
I would imagine that most of that weight is in the 1st 2nd and 3rd stage rockets and their fuel.
fuel weight would not be much of a factor if you dont need to expend much fuel for a lift off.
the remote vehicle itself could return to the platform after
it has delivered its payload.
the platform could then be lowered back to ground level to await the next payload delivery by compressing the lifting gas into cylinders for later use.
and you could use solar power to operate the compressors and charge the battery arrays that are used to operate the electronics systems and subsystems.
the payloads could be supplies and building materials used to construct a expedition vehicle to the moon or mars or wherever.
you could use the ISS as a home base for the construction workers that are building the expedition vehicles.
the total cost would be greatly reduced.
and the re-useable platform and re-useable remote vehicle systems means you dont need to continuously expend great amounts of tax dollars , which converts into more accomplishments to every dollar expended.
plus we shouldn't pile all the responsibility of
payload duties on the russian's either.
