Orbital elevators and long, long days

[Agemegos]

My algorithm for determining what planets in my SF setting ought to have tower facilities (a.k.a. orbital elevators, a.k.a. beanstalks) takes into account economic volume and tech level, but not the cost of building the elevator. Now that I am using (modified) GURPS Space to generate more realistic star systems I am getting quite a lot with much, much longer days. And that means longer, more massive, more expensive elevators.

So what's the story? In the case of a planet that is tide-locked to one of its moons the geostationary orbit is at the moon's altitude, which means that the options are to build an elevator to the moon (allowing somehow for variations in its length and orientation if the moon's orbit is at all eccentric) or to build an elevator to L1, L3, L4, or L5. (In the case of a tide-locked habitable moon L1, L2, L4, and L5 are available.) In the case of a planet the solar L1, L2, L4, and L5 points are the only possible places for the centre of mass of an orbital elevator.

Intuition suggests to me that elevators to moons or to the Lagrange points, and especially to solar Lagrange points would be prohibitively expensive, and possibly impractical, perhaps even impossible at TL10. But intuition is notoriously unreliable. Has anyone seen studies?