The events are free but the lodging certainly isn't. Anything in Aspen if available will be at a premium at that time. I am not sure about how the other mountains are traffic wise. I've been there for some Dew Tour events and the other mountains were not any more or less crowded. Getting around town during the Xgames could be a challenge though and I would imagine parking sucks. Fortunately the bus service is free in the valley. You might look at staying in Basalt or Carbondale.