Check southwest, expedia, and kayak. I'd be surprised if you can book this early? When you do get to booking, remember that SW is about 50 bucks cheaper per person because they don't charge baggage fees. So, factor that into your decision-making. Anytime I've gone out to CO I've gotten 2wd (check carrentals.com) and it worked fine for me. That may save you a few bucks. I'm with the earlier poster, I prefer to have my own car to get around and check things out. I strongly suggest you do that, especially if you'll be there for 2 weeks. If you're there for that long you might want to wander around the area and check-out all that CO has to offer outside of the resorts!
Traveling the States and Taking Pictures