We took a day trip to Milford Sound from Queenstown using Kiwi Discovery. Milford is only about 50 miles west of Queenstown but there are no passable roads in that direction, thus a very roundabout route is required and the entire trip from pickup to return was about 13 hours. The other option to see Milford, from what I could tell, would be to stay in Te Anau, which is only about 2 hours away, but there was nothing there and we were happy about booking the all-day tour and keeping our base in Queenstown.
Our driver was Carlin, and he truly made the long day enjoyable, from telling stories, to providing a little history about Milford and New Zealand, to showing a movie on the way back. He also made stops along the way so that we could enjoy and take photos of some of the gorgeous NZ scenery.
Upon arriving at Milford Sound, we boarded a boat for a two hour cruise. It was a rather small boat which was nice with a small group. One thing I read on other reviews was the lunch option they provided was rather pricey and not good, so we opted to bring our own and there was plenty of space on the boat to sit down for a snack. I'd recommend bringing a light lunch and snacks, plus water and warm clothes as the boat was rather windy.
We found the price to be reasonable and really enjoyed our trip. We would recommend booking this tour with Kiwi Discovery if you are staying in Queenstown but would like to see Milford.