Well, Big Sky is not like a typical ski resort. The base area itself is small not good for much more than your post-ski, pre-dinner drink. The "town" of Big Sky is stretched out from the Gallatin River (start of road up to Big Sky) up to Moonlight Basin (just past Big Sky). Shuttles go all up and down the access road and run fairly late. Really no need to drive once you're there. So even if you end up seven miles away, close to the Gally, you can still grab the shuttle, which is what you'll have to do even if your half a mile away.
But for the better deals, you many want to check the condo rental sites and look for places in the "Meadow" area, which is down lower around the golf course (used to be a meadow, I guess), but still great views and kind of its own little town.
The car is good to have, though, if you don't want to wait outside for the last shuttle. And, who knows, you may get an itch and want to go to Bozeman or down to West Yellowstone.