The question How useful is placing an asteroid in the Moon's orbit? quotes a news article saying the Obama administration is opposed to a lunar landing mission because of the cost of such a mission:
The Obama administration is opposed to another moon landing, saying such a mission would be too costly. It wants instead to focus on capturing an asteroid and placing it into the Moon's orbit for future exploration.
But placing an asteroid in lunar orbit and going there to pay a visit to it isn't exactly cheap either (even if the delta-v to bring the asteroid into a lunar orbit isn't that large and everything goes perfectly, there's still the cost of first getting to the asteroid in its original orbit, then getting to lunar orbit to do anything with it). Sending robots to do the exploration and possibly mining of the asteroid would almost certainly cut down on the cost, but that same argument also holds for a lunar landing mission: technology has advanced a lot since the 1960s, so we can do a lot with robots today that we couldn't reasonably or even at all do back then. The difference in capability between the early planetary landing probe missions and the recent Mars missions, for example, shows this well.
All this got me wondering. If we assume for a second that we would want to go to the Moon in some manner, then roughly how much higher would the monetary cost be just to land on the Moon and getting back into lunar orbit, compared to only establishing a (reasonably) stable lunar orbit? It's probably safe to say that it would add a fair bit to the cost of the mission, but how much? Let's ignore the matter of human EVA capability; people aren't going to be walking around on the surface of the moon from a lunar orbit either (even though landing people on the Moon without human EVA capability seems a bit silly, to put it mildly; there isn't a lot that can be done by Moon-local remote control that can't be done over an Earth-Moon link, if only you have enough power and receiver sensitivity for a good quality downlink from the Moon), and a lot can be done without sending humans either to lunar orbit or to the lunar surface.
A good answer would explore this both from the angle of manned and unmanned missions. Order of magnitude figures are quite good enough.