I just did this. Same deal. Unfinished garage spot.
Put up some walls. Chose a Pergo solution for the flooring. Easy to install. About the same price a carpet. Looks great and sounds great. I did find it a little bright so I've put a rug and some curtains.
Overall, I'm very happy. It wasn't too expensive or too difficult (like floating the floor). I've run cables through the walls while building them. Everything works/sounds as it should, VERY GOOD.