Flying in?  Travelocity or Expedia can get you cheap flights to Bozeman, MT or BZN.   Avis or Budget Rental Cars (among others) are available at the airport, as well as the Big Sky Taxi or Karst Stage for your trip from the airport in Bozeman to Big Sky.

I found the Aspen Grove Cabin you were looking at...it is a private home and located in a good median area of Big Sky (between the river, golfcourse and the top of the mountain).  I have linked a few other places you may be interested in...