This is an AMAZING excursion! In May 2005 while sailing on NCL Star, I did a dogsled tour in Juneau. We took a helicopter out to Mendenhall (sp?) glacier, met the mushers, dogs and spent a few hours out there. We were able to lead a sled, mush, ride etc. It was the best time! Yes, it is expensive, but totally worth it.
Skagway I took the Whitepass Railway, another great tour.
Have a wonderful trip!