Charles F. Radley wrote:
Vincent,

Nice idea, but not original. Hoyt, Forward and Moravec have each proposed
using tethers for lunar landing and sample return some years ago.

It can be done even more cheaply than you propose.

You do not even need any ion drive or propulsion at all actually. You can
do it entirely with zero momentum exchange, you simply deposit payloads on
to the lunar surface whose mass equals that of the samples you remove.

Assuming a spherical moon.
For non-spherical, non-ideal gravity moons, things get more interesting.