Well, "most abundant" in the heterosphere doesn't really say much given that the density at those altitudes is sufficiently low that the molecules have a large

Well, "most abundant" in the heterosphere doesn't really say much given that the density at those altitudes is sufficiently low that the molecules have a large mean free path. We're basically talking satellite orbit altitudes here, so it would be seriously difficult to haul something large enough to gather enough mass to be useful. Certainly it wouldn't be cheap. And 3000 tons per year is not that much given that Wikipedia says "2008 world helium total production of about 32 million kg helium", ie 32000 metric tons. In other words, demand exceeds production by a factor of 10, even if (and that's a big if) all of the He in the lithosphere could be captured. No, I think the solution is to go to Jupiter and scoop up a huge load of it (gotta be Jupiter, Saturn's atmosphere is deficient in He). And given that we need it for spaceflight, better do it before we use it all up!