This is the one that I've been "leaning" toward as well, since at least a portion of the tour includes the official "line" between N and S, and I understand that its possible to have military personnel on the tour - which could be interesting in and of itself.

My understanding is that the cost is "near" 75,000 Won, not much different than others.
Advance resv are, of course, going to be required.

Best, Dave