Flying into Mammoth is not nearly as reasonably priced as the other areas mentioned, nor can it be as direct. You can say the same thing about Jackson, Aspen, Telluride, and many others. You can not say that there are direct flights from just about anywhere in the US to those airports though. Thus jacking up the price considerably to fly to those spots. Sorry, but Mammoth just doesn't work in that regard.
I like Tahoe. Have you looked into any of the prices before by chance