Re: Unaffordium, sorry.
The real problem, the real, true, brain-boggling problem with space flight is the cost of getting it from the surface of the planet Earth into orbit. The reason for this is that the cost of transport rises exponentially, because the amount of fuel you need to put that payload into orbit expands exponentially.
Once you get something into orbit, of course, you're half-way to anywhere. The problem is that unless you *only* want to go to orbit, any fuel (and engines, et cetera,) you need to do the rest of your stuff is now additional payload for the lift *into* orbit, and that's where everything goes wonky. I'm not really very learned at this, I can't bust out equations or sums, but if you want to get an *instinctive* grasp on this problem, go play with Kerbal Space Program for a while.
That's why the things we've launched further than the moon tend to be much, much *lighter* than the things we've taken into orbit. Even the 1960s-era space race budget wouldn't have been up to the task of sending something the size of the shuttles (themselves now decommissioned largely for budgetary reasons,) to Venus.
Of course, some dreams are basically impossible in terms that anyone living today will see, but others are not. I expect that, barring some kind of age-longevity treatment (which will of course be available primarily or exclusively to the rich, at first,) nobody alive today will live to see the fabled permanent sky-cities on Venus even seriously begin as a project beyond a bunch of futurists sitting around throwing ideas around. Seeing a man in orbit of or on the surface of Mars, though, perhaps. But far more likely would be some kind of installation built to exploit resources available in-situ on the Moon, and maybe some asteroid mining/retrieval programs, and if we're very lucky, the start of construction on a space elevator, which would make all of this *so much simpler*.
(As a side-note, exploiting resources available in-situ on the moon is a fantastic idea, because it means that you only have to lift your actual payload into earth orbit, then you can fit its engines and fuel which were made on the Moon, and were much easier to get /off/ the moon.)