The nice thing about the airpass is that you can use one-ways that would normally cost you more. But you also need to buy at least 3 flights, so that might be one more than you would need.
Looks to me that you would be better off first looking at what a round-trip LAX-NYC would cost. I assume you will be staying in Los Angeles, you will then most likely need a car and a trip to Las Vegas is a quick and easy one then.